--- a/browser/app/blocklist.xml
+++ b/browser/app/blocklist.xml
@@ -3926,16 +3926,19 @@
       <serialNumber>AINVG9I4T2jgQgW4N9SNhw==</serialNumber>
     </certItem>
     <certItem issuerName="MD4xCzAJBgNVBAYTAlBMMRswGQYDVQQKExJVbml6ZXRvIFNwLiB6IG8uby4xEjAQBgNVBAMTCUNlcnR1bSBDQQ==">
       <serialNumber>e7wSpVxmgAS5/ioLi2iBIA==</serialNumber>
     </certItem>
     <certItem issuerName="MFoxCzAJBgNVBAYTAklFMRIwEAYDVQQKEwlCYWx0aW1vcmUxEzARBgNVBAsTCkN5YmVyVHJ1c3QxIjAgBgNVBAMTGUJhbHRpbW9yZSBDeWJlclRydXN0IFJvb3Q=">
       <serialNumber>Byemag==</serialNumber>
     </certItem>
+    <certItem issuerName="MEoxCzAJBgNVBAYTAlVTMRYwFAYDVQQKEw1MZXQncyBFbmNyeXB0MSMwIQYDVQQDExpMZXQncyBFbmNyeXB0IEF1dGhvcml0eSBYMw==">
+      <serialNumber>AxPlMqxkByCn3XNuYMhYNMcp</serialNumber>
+    </certItem>
     <certItem issuerName="MIHKMQswCQYDVQQGEwJVUzEXMBUGA1UEChMOVmVyaVNpZ24sIEluYy4xHzAdBgNVBAsTFlZlcmlTaWduIFRydXN0IE5ldHdvcmsxOjA4BgNVBAsTMShjKSAyMDA3IFZlcmlTaWduLCBJbmMuIC0gRm9yIGF1dGhvcml6ZWQgdXNlIG9ubHkxRTBDBgNVBAMTPFZlcmlTaWduIENsYXNzIDMgUHVibGljIFByaW1hcnkgQ2VydGlmaWNhdGlvbiBBdXRob3JpdHkgLSBHNA==">
       <serialNumber>cXXMzbWDHMIdCotb3h64yw==</serialNumber>
     </certItem>
     <certItem issuerName="MF8xCzAJBgNVBAYTAlVTMRcwFQYDVQQKEw5WZXJpU2lnbiwgSW5jLjE3MDUGA1UECxMuQ2xhc3MgMyBQdWJsaWMgUHJpbWFyeSBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0eQ==">
       <serialNumber>E/YGRk12iZqZuMfsIiVaeg==</serialNumber>
     </certItem>
     <certItem issuerName="MFoxCzAJBgNVBAYTAklFMRIwEAYDVQQKEwlCYWx0aW1vcmUxEzARBgNVBAsTCkN5YmVyVHJ1c3QxIjAgBgNVBAMTGUJhbHRpbW9yZSBDeWJlclRydXN0IFJvb3Q=">
       <serialNumber>Bye2Cg==</serialNumber>
@@ -4067,25 +4070,16 @@
       <serialNumber>AQw=</serialNumber>
     </certItem>
     <certItem issuerName="MIGVMQswCQYDVQQGEwJHUjFEMEIGA1UEChM7SGVsbGVuaWMgQWNhZGVtaWMgYW5kIFJlc2VhcmNoIEluc3RpdHV0aW9ucyBDZXJ0LiBBdXRob3JpdHkxQDA+BgNVBAMTN0hlbGxlbmljIEFjYWRlbWljIGFuZCBSZXNlYXJjaCBJbnN0aXR1dGlvbnMgUm9vdENBIDIwMTE=">
       <serialNumber>FJl6tXgNpSk=</serialNumber>
     </certItem>
     <certItem issuerName="MHExKDAmBgNVBAMTH0dsb2JhbFNpZ24gUm9vdFNpZ24gUGFydG5lcnMgQ0ExHTAbBgNVBAsTFFJvb3RTaWduIFBhcnRuZXJzIENBMRkwFwYDVQQKExBHbG9iYWxTaWduIG52LXNhMQswCQYDVQQGEwJCRQ==">
       <serialNumber>BAAAAAAA+X/GIyk=</serialNumber>
     </certItem>
-    <certItem issuerName="MIHBMQswCQYDVQQGEwJVUzEXMBUGA1UEChMOVmVyaVNpZ24sIEluYy4xPDA6BgNVBAsTM0NsYXNzIDMgUHVibGljIFByaW1hcnkgQ2VydGlmaWNhdGlvbiBBdXRob3JpdHkgLSBHMjE6MDgGA1UECxMxKGMpIDE5OTggVmVyaVNpZ24sIEluYy4gLSBGb3IgYXV0aG9yaXplZCB1c2Ugb25seTEfMB0GA1UECxMWVmVyaVNpZ24gVHJ1c3QgTmV0d29yaw==">
-      <serialNumber>O2Qh+qhbBRuZA11yDhcLGQ==</serialNumber>
-    </certItem>
-    <certItem issuerName="MFwxCzAJBgNVBAYTAkJFMRUwEwYDVQQLEwxUcnVzdGVkIFJvb3QxGTAXBgNVBAoTEEdsb2JhbFNpZ24gbnYtc2ExGzAZBgNVBAMTElRydXN0ZWQgUm9vdCBDQSBHMg==">
-      <serialNumber>UU3AP1SMxmyhBFq7MRFZmf0=</serialNumber>
-    </certItem>
-    <certItem issuerName="MF8xCzAJBgNVBAYTAkJFMRkwFwYDVQQKExBHbG9iYWxTaWduIG52LXNhMRQwEgYDVQQLEwtQYXJ0bmVycyBDQTEfMB0GA1UEAxMWR2xvYmFsU2lnbiBQYXJ0bmVycyBDQQ==">
-      <serialNumber>BAAAAAABHhw1vwc=</serialNumber>
-    </certItem>
     <certItem issuerName="MD0xCzAJBgNVBAYTAkZSMREwDwYDVQQKEwhDZXJ0cGx1czEbMBkGA1UEAxMSQ2xhc3MgMiBQcmltYXJ5IENB">
       <serialNumber>ESDItX4ruWiLnrlz0rk4/bmz</serialNumber>
     </certItem>
     <certItem issuerName="MEwxIDAeBgNVBAsTF0dsb2JhbFNpZ24gUm9vdCBDQSAtIFIyMRMwEQYDVQQKEwpHbG9iYWxTaWduMRMwEQYDVQQDEwpHbG9iYWxTaWdu">
       <serialNumber>BAAAAAABIg08D3U=</serialNumber>
     </certItem>
     <certItem issuerName="MIGVMQswCQYDVQQGEwJHUjFEMEIGA1UEChM7SGVsbGVuaWMgQWNhZGVtaWMgYW5kIFJlc2VhcmNoIEluc3RpdHV0aW9ucyBDZXJ0LiBBdXRob3JpdHkxQDA+BgNVBAMTN0hlbGxlbmljIEFjYWRlbWljIGFuZCBSZXNlYXJjaCBJbnN0aXR1dGlvbnMgUm9vdENBIDIwMTE=">
       <serialNumber>GN2Hrh9LtnI=</serialNumber>
@@ -4799,10 +4793,19 @@
       <serialNumber>BAAAAAABK84yjs8=</serialNumber>
     </certItem>
     <certItem issuerName="MD0xCzAJBgNVBAYTAkZSMREwDwYDVQQKEwhDZXJ0cGx1czEbMBkGA1UEAxMSQ2xhc3MgMiBQcmltYXJ5IENB">
       <serialNumber>ESCC9oPNcRdPOox+SjWm9dTX</serialNumber>
     </certItem>
     <certItem issuerName="MD0xCzAJBgNVBAYTAkZSMREwDwYDVQQKEwhDZXJ0cGx1czEbMBkGA1UEAxMSQ2xhc3MgMiBQcmltYXJ5IENB">
       <serialNumber>DjIvBkX+ECVbB/C3i6w2Gg==</serialNumber>
     </certItem>
+    <certItem issuerName="MIHBMQswCQYDVQQGEwJVUzEXMBUGA1UEChMOVmVyaVNpZ24sIEluYy4xPDA6BgNVBAsTM0NsYXNzIDMgUHVibGljIFByaW1hcnkgQ2VydGlmaWNhdGlvbiBBdXRob3JpdHkgLSBHMjE6MDgGA1UECxMxKGMpIDE5OTggVmVyaVNpZ24sIEluYy4gLSBGb3IgYXV0aG9yaXplZCB1c2Ugb25seTEfMB0GA1UECxMWVmVyaVNpZ24gVHJ1c3QgTmV0d29yaw==">
+      <serialNumber>O2Qh+qhbBRuZA11yDhcLGQ==</serialNumber>
+    </certItem>
+    <certItem issuerName="MFwxCzAJBgNVBAYTAkJFMRUwEwYDVQQLEwxUcnVzdGVkIFJvb3QxGTAXBgNVBAoTEEdsb2JhbFNpZ24gbnYtc2ExGzAZBgNVBAMTElRydXN0ZWQgUm9vdCBDQSBHMg==">
+      <serialNumber>UU3AP1SMxmyhBFq7MRFZmf0=</serialNumber>
+    </certItem>
+    <certItem issuerName="MF8xCzAJBgNVBAYTAkJFMRkwFwYDVQQKExBHbG9iYWxTaWduIG52LXNhMRQwEgYDVQQLEwtQYXJ0bmVycyBDQTEfMB0GA1UEAxMWR2xvYmFsU2lnbiBQYXJ0bmVycyBDQQ==">
+      <serialNumber>BAAAAAABHhw1vwc=</serialNumber>
+    </certItem>
   </certItems>
 </blocklist>

--- a/browser/base/content/browser-thumbnails.js
+++ b/browser/base/content/browser-thumbnails.js
@@ -39,17 +39,16 @@ var gBrowserThumbnails = {
   _topSiteURLsRefreshTimer: null,
 
   /**
    * List of tab events we want to listen for.
    */
   _tabEvents: ["TabClose", "TabSelect"],
 
   init: function Thumbnails_init() {
-    PageThumbs.addExpirationFilter(this);
     gBrowser.addTabsProgressListener(this);
     Services.prefs.addObserver(this.PREF_DISK_CACHE_SSL, this);
     Services.prefs.addObserver(this.PREF_ACTIVITY_STREAM_ENABLED, this);
 
     this._sslDiskCacheEnabled =
       Services.prefs.getBoolPref(this.PREF_DISK_CACHE_SSL);
     this._activityStreamEnabled =
       Services.prefs.getBoolPref(this.PREF_ACTIVITY_STREAM_ENABLED);
@@ -57,17 +56,16 @@ var gBrowserThumbnails = {
     this._tabEvents.forEach(function(aEvent) {
       gBrowser.tabContainer.addEventListener(aEvent, this);
     }, this);
 
     this._timeouts = new WeakMap();
   },
 
   uninit: function Thumbnails_uninit() {
-    PageThumbs.removeExpirationFilter(this);
     gBrowser.removeTabsProgressListener(this);
     Services.prefs.removeObserver(this.PREF_DISK_CACHE_SSL, this);
     Services.prefs.removeObserver(this.PREF_ACTIVITY_STREAM_ENABLED, this);
 
     if (this._topSiteURLsRefreshTimer) {
       this._topSiteURLsRefreshTimer.cancel();
       this._topSiteURLsRefreshTimer = null;
     }
@@ -99,46 +97,36 @@ var gBrowserThumbnails = {
       case this.PREF_DISK_CACHE_SSL:
         this._sslDiskCacheEnabled =
           Services.prefs.getBoolPref(this.PREF_DISK_CACHE_SSL);
         break;
       case this.PREF_ACTIVITY_STREAM_ENABLED:
         this._activityStreamEnabled =
           Services.prefs.getBoolPref(this.PREF_ACTIVITY_STREAM_ENABLED);
         // Get the new top sites
-        XPCOMUtils.defineLazyGetter(this, "_topSiteURLs", getTopSiteURLs);
+        this.clearTopSiteURLCache();
         break;
     }
   },
 
-  /**
-   * clearTopSiteURLCache is only ever called if we've created an nsITimer,
-   * which only happens if we've loaded the tiles top sites. Therefore we only
-   * need to clear the tiles top sites (and not activity stream's top sites)
-   */
   clearTopSiteURLCache: function Thumbnails_clearTopSiteURLCache() {
     if (this._topSiteURLsRefreshTimer) {
       this._topSiteURLsRefreshTimer.cancel();
       this._topSiteURLsRefreshTimer = null;
     }
     // Delete the defined property
     delete this._topSiteURLs;
     XPCOMUtils.defineLazyGetter(this, "_topSiteURLs", getTopSiteURLs);
   },
 
   notify: function Thumbnails_notify(timer) {
     gBrowserThumbnails._topSiteURLsRefreshTimer = null;
     gBrowserThumbnails.clearTopSiteURLCache();
   },
 
-  async filterForThumbnailExpiration(aCallback) {
-    const topSites = await this._topSiteURLs;
-    aCallback(topSites);
-  },
-
   /**
    * State change progress listener for all tabs.
    */
   onStateChange: function Thumbnails_onStateChange(aBrowser, aWebProgress,
                                                    aRequest, aStateFlags, aStatus) {
     if (aStateFlags & Ci.nsIWebProgressListener.STATE_STOP &&
         aStateFlags & Ci.nsIWebProgressListener.STATE_IS_NETWORK)
       this._delayedCapture(aBrowser);
@@ -207,28 +195,33 @@ var gBrowserThumbnails = {
     } else {
       // idle callback dispatched
       window.cancelIdleCallback(timeoutData.id);
     }
   }
 };
 
 async function getTopSiteURLs() {
+  // The _topSiteURLs getter can be expensive to run, but its return value can
+  // change frequently on new profiles, so as a compromise we cache its return
+  // value as a lazy getter for 1 minute every time it's called.
+  gBrowserThumbnails._topSiteURLsRefreshTimer =
+    Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
+  gBrowserThumbnails._topSiteURLsRefreshTimer.initWithCallback(gBrowserThumbnails,
+                                                               60 * 1000,
+                                                               Ci.nsITimer.TYPE_ONE_SHOT);
   let sites = [];
   if (gBrowserThumbnails._activityStreamEnabled) {
-    sites = await NewTabUtils.activityStreamLinks.getTopSites();
+    // Get both the top sites returned by the query, and also any pinned sites
+    // that the user might have added manually that also need a screenshot.
+    // Also include top sites that don't have rich icons
+    let topSites = await NewTabUtils.activityStreamLinks.getTopSites();
+    sites.push(...topSites.filter(link => !(link.faviconSize >= 96)));
+    sites.push(...NewTabUtils.pinnedLinks.links);
   } else {
-    // The _topSiteURLs getter can be expensive to run, but its return value can
-    // change frequently on new profiles, so as a compromise we cache its return
-    // value as a lazy getter for 1 minute every time it's called.
-    gBrowserThumbnails._topSiteURLsRefreshTimer =
-      Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
-    gBrowserThumbnails._topSiteURLsRefreshTimer.initWithCallback(gBrowserThumbnails,
-                                                                 60 * 1000,
-                                                                 Ci.nsITimer.TYPE_ONE_SHOT);
     sites = NewTabUtils.links.getLinks();
   }
   return sites.reduce((urls, link) => {
     if (link) urls.push(link.url);
     return urls;
   }, []);
 }
 

--- a/browser/base/content/tabbrowser.xml
+++ b/browser/base/content/tabbrowser.xml
@@ -255,17 +255,17 @@
 
           if (aTab.hidden)
             this.showTab(aTab);
 
           this.moveTabTo(aTab, this._numPinnedTabs);
           aTab.setAttribute("pinned", "true");
           this.tabContainer._unlockTabSizing();
           this.tabContainer._positionPinnedTabs();
-          this.tabContainer.adjustTabstrip();
+          this.tabContainer._updateCloseButtons();
 
           this.getBrowserForTab(aTab).messageManager.sendAsyncMessage("Browser:AppTab", { isAppTab: true })
 
           if (aTab.selected)
             this._setCloseKeyState(false);
 
           let event = document.createEvent("Events");
           event.initEvent("TabPinned", true, false);
@@ -279,17 +279,17 @@
           if (!aTab.pinned)
             return;
 
           this.moveTabTo(aTab, this._numPinnedTabs - 1);
           aTab.removeAttribute("pinned");
           aTab.style.marginInlineStart = "";
           this.tabContainer._unlockTabSizing();
           this.tabContainer._positionPinnedTabs();
-          this.tabContainer.adjustTabstrip();
+          this.tabContainer._updateCloseButtons();
 
           this.getBrowserForTab(aTab).messageManager.sendAsyncMessage("Browser:AppTab", { isAppTab: false })
 
           if (aTab.selected)
             this._setCloseKeyState(true);
 
           let event = document.createEvent("Events");
           event.initEvent("TabUnpinned", true, false);
@@ -3351,17 +3351,17 @@
               this._windowIsClosing = true;
               while (this._removingTabs.length)
                 this._endRemoveTab(this._removingTabs[0]);
             } else if (!this._windowIsClosing) {
               if (aNewTab)
                 focusAndSelectUrlBar();
 
               // workaround for bug 345399
-              this.tabContainer.mTabstrip._updateScrollButtonsDisabledState();
+              this.tabContainer.arrowScrollbox._updateScrollButtonsDisabledState();
             }
 
             // We're going to remove the tab and the browser now.
             this._tabFilters.delete(aTab);
             this._tabListeners.delete(aTab);
 
             var browser = this.getBrowserForTab(aTab);
 
@@ -3388,17 +3388,17 @@
             for (let i = aTab._tPos; i < this.tabs.length; i++)
               this.tabs[i]._tPos = i;
 
             if (!this._windowIsClosing) {
               if (wasPinned)
                 this.tabContainer._positionPinnedTabs();
 
               // update tab close buttons state
-              this.tabContainer.adjustTabstrip();
+              this.tabContainer._updateCloseButtons();
 
               setTimeout(function(tabs) {
                 tabs._lastTabClosedByMouse = false;
               }, 0, this.tabContainer);
             }
 
             // update tab positional properties and attributes
             this.selectedTab._selected = true;
@@ -3862,17 +3862,17 @@
       <method name="showTab">
         <parameter name="aTab"/>
         <body>
         <![CDATA[
           if (aTab.hidden) {
             aTab.removeAttribute("hidden");
             this._visibleTabs = null; // invalidate cache
 
-            this.tabContainer.adjustTabstrip();
+            this.tabContainer._updateCloseButtons();
 
             this.tabContainer._setPositionalAttributes();
 
             let event = document.createEvent("Events");
             event.initEvent("TabShow", true, false);
             aTab.dispatchEvent(event);
           }
         ]]>
@@ -3883,17 +3883,17 @@
         <parameter name="aTab"/>
         <body>
         <![CDATA[
           if (!aTab.hidden && !aTab.pinned && !aTab.selected &&
               !aTab.closing) {
             aTab.setAttribute("hidden", "true");
             this._visibleTabs = null; // invalidate cache
 
-            this.tabContainer.adjustTabstrip();
+            this.tabContainer._updateCloseButtons();
 
             this.tabContainer._setPositionalAttributes();
 
             let event = document.createEvent("Events");
             event.initEvent("TabHide", true, false);
             aTab.dispatchEvent(event);
           }
         ]]>
@@ -6398,17 +6398,17 @@
         <xul:spacer class="closing-tabs-spacer" anonid="closing-tabs-spacer"
                     style="width: 0;"/>
       </xul:arrowscrollbox>
     </content>
 
     <implementation implements="nsIDOMEventListener, nsIObserver">
       <constructor>
         <![CDATA[
-          this.mTabClipWidth = Services.prefs.getIntPref("browser.tabs.tabClipWidth");
+          this._tabClipWidth = Services.prefs.getIntPref("browser.tabs.tabClipWidth");
 
           let { restoreTabsButton } = this;
           restoreTabsButton.setAttribute("label", gTabBrowserBundle.GetStringFromName("tabs.restoreLastTabs"));
 
           var tab = this.firstChild;
           tab.label = gTabBrowserBundle.GetStringFromName("tabs.emptyTabTitle");
           tab.setAttribute("onerror", "this.removeAttribute('image');");
 
@@ -6435,17 +6435,17 @@
       <field name="tabbox" readonly="true">
         this.tabbrowser.mTabBox;
       </field>
 
       <field name="contextMenu" readonly="true">
         document.getElementById("tabContextMenu");
       </field>
 
-      <field name="mTabstrip">
+      <field name="arrowScrollbox">
         document.getAnonymousElementByAttribute(this, "anonid", "arrowscrollbox");
       </field>
 
       <field name="_firstTab">null</field>
       <field name="_lastTab">null</field>
       <field name="_beforeSelectedTab">null</field>
       <field name="_beforeHoveredTab">null</field>
       <field name="_afterHoveredTab">null</field>
@@ -6474,33 +6474,33 @@
           let {restoreTabsButton, restoreTabsButtonWrapperWidth, windowUtils} = this;
           let restoreTabsButtonWrapper = restoreTabsButton.parentNode;
 
           if (!restoreTabsButtonWrapper.getAttribute("session-exists")) {
             restoreTabsButtonWrapper.removeAttribute("shown");
             return;
           }
 
-          let tabstripWidth = this.mTabstrip.clientWidth;
+          let arrowScrollboxWidth = this.arrowScrollbox.clientWidth;
 
           let newTabButton = document.getAnonymousElementByAttribute(
             this, "anonid", "tabs-newtab-button");
 
           // If there are no pinned tabs it will multiply by 0 and result in 0
           let pinnedTabsWidth = windowUtils.getBoundsWithoutFlushing(this.firstChild).width * this._lastNumPinned;
 
           let numUnpinnedTabs = this.childNodes.length - this._lastNumPinned;
           let unpinnedTabsWidth = windowUtils.getBoundsWithoutFlushing(this.lastChild).width * numUnpinnedTabs;
 
           let tabbarUsedSpace = pinnedTabsWidth + unpinnedTabsWidth
             + windowUtils.getBoundsWithoutFlushing(newTabButton).width;
 
           // Subtract the elements' widths from the available space to ensure
           // that showing the restoreTabsButton won't cause any overflow.
-          if (tabstripWidth - tabbarUsedSpace > restoreTabsButtonWrapperWidth) {
+          if (arrowScrollboxWidth - tabbarUsedSpace > restoreTabsButtonWrapperWidth) {
             restoreTabsButtonWrapper.setAttribute("shown", "true");
           } else {
             restoreTabsButtonWrapper.removeAttribute("shown");
           }
         ]]></body>
       </method>
 
       <method name="observe">
@@ -6666,17 +6666,17 @@
           if (this.childNodes.length - this.tabbrowser._removingTabs.length == 1)
             this.visible = window.toolbar.visible;
           else
             this.visible = true;
         ]]></body>
       </method>
 
       <field name="_closeButtonsUpdatePending">false</field>
-      <method name="adjustTabstrip">
+      <method name="_updateCloseButtons">
         <body><![CDATA[
           // If we're overflowing, tabs are at their minimum widths.
           if (this.getAttribute("overflow") == "true") {
             this.setAttribute("closebuttons", "activetab");
             return;
           }
 
           if (this._closeButtonsUpdatePending) {
@@ -6701,31 +6701,31 @@
               // remove close buttons from background tabs so that people don't
               // accidentally close tabs by selecting them.
               let rect = ele => {
                 return window.QueryInterface(Ci.nsIInterfaceRequestor)
                              .getInterface(Ci.nsIDOMWindowUtils)
                              .getBoundsWithoutFlushing(ele);
               };
               let tab = this.tabbrowser.visibleTabs[this.tabbrowser._numPinnedTabs];
-              if (tab && rect(tab).width <= this.mTabClipWidth) {
+              if (tab && rect(tab).width <= this._tabClipWidth) {
                 this.setAttribute("closebuttons", "activetab");
               } else {
                 this.removeAttribute("closebuttons");
               }
             });
           });
         ]]></body>
       </method>
 
       <method name="_handleTabSelect">
         <parameter name="aInstant"/>
         <body><![CDATA[
           if (this.getAttribute("overflow") == "true")
-            this.mTabstrip.ensureElementIsVisible(this.selectedItem, aInstant);
+            this.arrowScrollbox.ensureElementIsVisible(this.selectedItem, aInstant);
 
           this.selectedItem._notselectedsinceload = false;
         ]]></body>
       </method>
 
       <field name="_closingTabsSpacer">
         document.getAnonymousElementByAttribute(this, "anonid", "closing-tabs-spacer");
       </field>
@@ -6748,17 +6748,17 @@
           if (!this._tabDefaultMaxWidth)
             this._tabDefaultMaxWidth =
               parseFloat(window.getComputedStyle(aTab).maxWidth);
           this._lastTabClosedByMouse = true;
 
           if (this.getAttribute("overflow") == "true") {
             // Don't need to do anything if we're in overflow mode and aren't scrolled
             // all the way to the right, or if we're closing the last tab.
-            if (isEndTab || !this.mTabstrip._scrollButtonDown.disabled)
+            if (isEndTab || !this.arrowScrollbox._scrollButtonDown.disabled)
               return;
 
             // If the tab has an owner that will become the active tab, the owner will
             // be to the left of it, so we actually want the left tab to slide over.
             // This can't be done as easily in non-overflow mode, so we don't bother.
             if (aTab.owner)
               return;
 
@@ -6833,20 +6833,20 @@
           var doPosition = this.getAttribute("overflow") == "true" &&
                            numPinned > 0;
 
           if (doPosition) {
             this.setAttribute("positionpinnedtabs", "true");
 
             let layoutData = this._pinnedTabsLayoutCache;
             if (!layoutData) {
-              let tabstrip = this.mTabstrip;
+              let arrowScrollbox = this.arrowScrollbox;
               layoutData = this._pinnedTabsLayoutCache = {
                 pinnedTabWidth: this.childNodes[0].getBoundingClientRect().width,
-                scrollButtonWidth: tabstrip._scrollButtonDown.getBoundingClientRect().width
+                scrollButtonWidth: arrowScrollbox._scrollButtonDown.getBoundingClientRect().width
               };
             }
 
             let width = 0;
             for (let i = numPinned - 1; i >= 0; i--) {
               let tab = this.childNodes[i];
               width += layoutData.pinnedTabWidth;
               tab.style.marginInlineStart = -(width + layoutData.scrollButtonWidth) + "px";
@@ -6903,17 +6903,17 @@
 
           // Move the dragged tab based on the mouse position.
 
           let leftTab = tabs[0];
           let rightTab = tabs[tabs.length - 1];
           let tabScreenX = draggedTab.boxObject.screenX;
           let translateX = screenX - draggedTab._dragData.screenX;
           if (!pinned)
-            translateX += this.mTabstrip._scrollbox.scrollLeft - draggedTab._dragData.scrollX;
+            translateX += this.arrowScrollbox._scrollbox.scrollLeft - draggedTab._dragData.scrollX;
           let leftBound = leftTab.boxObject.screenX - tabScreenX;
           let rightBound = (rightTab.boxObject.screenX + rightTab.boxObject.width) -
                            (tabScreenX + tabWidth);
           translateX = Math.max(translateX, leftBound);
           translateX = Math.min(translateX, rightBound);
           draggedTab.style.transform = "translateX(" + translateX + "px)";
           draggedTab._dragData.translateX = translateX;
 
@@ -6995,17 +6995,17 @@
               this.updateVisibility();
               TabsInTitlebar.init();
               break;
             case "resize":
               if (aEvent.target != window)
                 break;
 
               TabsInTitlebar.updateAppearance();
-              this.adjustTabstrip();
+              this._updateCloseButtons();
               this._handleTabSelect(true);
               this.updateSessionRestoreVisibility();
               break;
             case "mouseout":
               // If the "related target" (the node to which the pointer went) is not
               // a child of the current document, the mouse just left the window.
               let relatedTarget = aEvent.relatedTarget;
               if (relatedTarget && relatedTarget.ownerDocument == document)
@@ -7014,50 +7014,50 @@
               if (document.getElementById("tabContextMenu").state != "open")
                 this._unlockTabSizing();
               break;
           }
         ]]></body>
       </method>
 
       <field name="_animateElement">
-        this.mTabstrip._scrollButtonDown;
+        this.arrowScrollbox._scrollButtonDown;
       </field>
 
       <method name="_notifyBackgroundTab">
         <parameter name="aTab"/>
         <body><![CDATA[
           if (aTab.pinned || aTab.hidden)
             return;
 
-          var scrollRect = this.mTabstrip.scrollClientRect;
+          var scrollRect = this.arrowScrollbox.scrollClientRect;
           var tab = aTab.getBoundingClientRect();
 
           // DOMRect left/right properties are immutable.
           tab = {left: tab.left, right: tab.right};
 
           // Is the new tab already completely visible?
           if (scrollRect.left <= tab.left && tab.right <= scrollRect.right)
             return;
 
-          if (this.mTabstrip.smoothScroll) {
+          if (this.arrowScrollbox.smoothScroll) {
             let selected = !this.selectedItem.pinned &&
                            this.selectedItem.getBoundingClientRect();
 
             // Can we make both the new tab and the selected tab completely visible?
             if (!selected ||
                 Math.max(tab.right - selected.left, selected.right - tab.left) <=
                   scrollRect.width) {
-              this.mTabstrip.ensureElementIsVisible(aTab);
+              this.arrowScrollbox.ensureElementIsVisible(aTab);
               return;
             }
 
-            this.mTabstrip.scrollByPixels(this.mTabstrip._isRTLScrollbox ?
-                                          selected.right - scrollRect.right :
-                                          selected.left - scrollRect.left);
+            this.arrowScrollbox.scrollByPixels(this.arrowScrollbox._isRTLScrollbox ?
+                                                 selected.right - scrollRect.right :
+                                                 selected.left - scrollRect.left);
           }
 
           if (!this._animateElement.hasAttribute("highlight")) {
             this._animateElement.setAttribute("highlight", "true");
             setTimeout(function(ele) {
               ele.removeAttribute("highlight");
             }, 150, this._animateElement);
           }
@@ -7137,30 +7137,30 @@
       <method name="_handleNewTab">
         <parameter name="tab"/>
         <body><![CDATA[
           if (tab.parentNode != this)
             return;
           tab._fullyOpen = true;
           this.tabbrowser.tabAnimationsInProgress--;
 
-          this.adjustTabstrip();
+          this._updateCloseButtons();
 
           if (tab.getAttribute("selected") == "true") {
             this._handleTabSelect();
           } else if (!tab.hasAttribute("skipbackgroundnotify")) {
             this._notifyBackgroundTab(tab);
           }
 
           // XXXmano: this is a temporary workaround for bug 345399
           // We need to manually update the scroll buttons disabled state
           // if a tab was inserted to the overflow area or removed from it
           // without any scrolling and when the tabbar has already
           // overflowed.
-          this.mTabstrip._updateScrollButtonsDisabledState();
+          this.arrowScrollbox._updateScrollButtonsDisabledState();
 
           // Preload the next about:newtab if there isn't one already.
           this.tabbrowser._createPreloadBrowser();
         ]]></body>
       </method>
 
       <method name="_canAdvanceToTab">
         <parameter name="aTab"/>
@@ -7193,17 +7193,17 @@
       <handler event="transitionend"><![CDATA[
         if (event.propertyName != "max-width")
           return;
 
         var tab = event.target;
 
         if (tab.getAttribute("fadein") == "true") {
           if (tab._fullyOpen)
-            this.adjustTabstrip();
+            this._updateCloseButtons();
           else
             this._handleNewTab(tab);
         } else if (tab.closing) {
           this.tabbrowser._endRemoveTab(tab);
         }
       ]]></handler>
 
       <handler event="dblclick"><![CDATA[
@@ -7443,17 +7443,17 @@
         // relative to the corner of the dragged tab.
         function clientX(ele) {
           return ele.getBoundingClientRect().left;
         }
         let tabOffsetX = clientX(tab) - clientX(this);
         tab._dragData = {
           offsetX: event.screenX - window.screenX - tabOffsetX,
           offsetY: event.screenY - window.screenY,
-          scrollX: this.mTabstrip._scrollbox.scrollLeft,
+          scrollX: this.arrowScrollbox._scrollbox.scrollLeft,
           screenX: event.screenX
         };
 
         event.stopPropagation();
       ]]></handler>
 
       <handler event="dragover"><![CDATA[
         var effects = this._getDropEffectForTabDrag(event);
@@ -7461,35 +7461,35 @@
         var ind = this._tabDropIndicator;
         if (effects == "" || effects == "none") {
           ind.collapsed = true;
           return;
         }
         event.preventDefault();
         event.stopPropagation();
 
-        var tabStrip = this.mTabstrip;
+        var arrowScrollbox = this.arrowScrollbox;
         var ltr = (window.getComputedStyle(this).direction == "ltr");
 
         // autoscroll the tab strip if we drag over the scroll
         // buttons, even if we aren't dragging a tab, but then
         // return to avoid drawing the drop indicator
         var pixelsToScroll = 0;
         if (this.getAttribute("overflow") == "true") {
           var targetAnonid = event.originalTarget.getAttribute("anonid");
           switch (targetAnonid) {
             case "scrollbutton-up":
-              pixelsToScroll = tabStrip.scrollIncrement * -1;
+              pixelsToScroll = arrowScrollbox.scrollIncrement * -1;
               break;
             case "scrollbutton-down":
-              pixelsToScroll = tabStrip.scrollIncrement;
+              pixelsToScroll = arrowScrollbox.scrollIncrement;
               break;
           }
           if (pixelsToScroll)
-            tabStrip.scrollByPixels((ltr ? 1 : -1) * pixelsToScroll, true);
+            arrowScrollbox.scrollByPixels((ltr ? 1 : -1) * pixelsToScroll, true);
         }
 
         if (effects == "move" &&
             this == event.dataTransfer.mozGetDataAt(TAB_DROP_TYPE, 0).parentNode) {
           ind.collapsed = true;
           this._animateTabMove(event);
           return;
         }
@@ -7503,22 +7503,22 @@
               this._dragTime = Date.now();
             if (Date.now() >= this._dragTime + this._dragOverDelay)
               this.selectedItem = tab;
             ind.collapsed = true;
             return;
           }
         }
 
-        var rect = tabStrip.getBoundingClientRect();
+        var rect = arrowScrollbox.getBoundingClientRect();
         var newMargin;
         if (pixelsToScroll) {
           // if we are scrolling, put the drop indicator at the edge
           // so that it doesn't jump while scrolling
-          let scrollRect = tabStrip.scrollClientRect;
+          let scrollRect = arrowScrollbox.scrollClientRect;
           let minMargin = scrollRect.left - rect.left;
           let maxMargin = Math.min(minMargin + scrollRect.width,
                                    scrollRect.right);
           if (!ltr)
             [minMargin, maxMargin] = [this.clientWidth - maxMargin,
                                       this.clientWidth - minMargin];
           newMargin = (pixelsToScroll > 0) ? maxMargin : minMargin;
         } else {
@@ -7666,17 +7666,17 @@
         }
 
         // Disable detach within the browser toolbox
         var eX = event.screenX;
         var eY = event.screenY;
         var wX = window.screenX;
         // check if the drop point is horizontally within the window
         if (eX > wX && eX < (wX + window.outerWidth)) {
-          let bo = this.mTabstrip.boxObject;
+          let bo = this.arrowScrollbox.boxObject;
           // also avoid detaching if the the tab was dropped too close to
           // the tabbar (half a tab)
           let endScreenY = bo.screenY + 1.5 * bo.height;
           if (eY < endScreenY && eY > window.screenY)
             return;
         }
 
         // screen.availLeft et. al. only check the screen that this window is on,
@@ -8245,26 +8245,26 @@
           var tabContainer = gBrowser.tabContainer;
           // We don't want menu item decoration unless there is overflow.
           if (tabContainer.getAttribute("overflow") != "true") {
             return;
           }
 
           let windowUtils = window.QueryInterface(Ci.nsIInterfaceRequestor)
                                   .getInterface(Ci.nsIDOMWindowUtils);
-          let tabstripRect = windowUtils.getBoundsWithoutFlushing(tabContainer.mTabstrip);
+          let arrowScrollboxRect = windowUtils.getBoundsWithoutFlushing(tabContainer.arrowScrollbox);
           for (let menuitem of this.childNodes) {
             let curTab = menuitem.tab;
             if (!curTab) {
               // "Undo close tab", menuseparator, or entries put here by addons.
               continue;
             }
             let curTabRect = windowUtils.getBoundsWithoutFlushing(curTab);
-            if (curTabRect.left >= tabstripRect.left &&
-                curTabRect.right <= tabstripRect.right) {
+            if (curTabRect.left >= arrowScrollboxRect.left &&
+                curTabRect.right <= arrowScrollboxRect.right) {
               menuitem.setAttribute("tabIsVisible", "true");
             } else {
               menuitem.removeAttribute("tabIsVisible");
             }
           }
         ]]></body>
       </method>
 

--- a/browser/base/content/test/performance/browser.ini
+++ b/browser/base/content/test/performance/browser.ini
@@ -14,12 +14,12 @@ skip-if = !e10s
 [browser_tabopen_reflows.js]
 [browser_tabopen_squeeze_reflows.js]
 [browser_tabstrip_overflow_underflow_reflows.js]
 [browser_tabswitch_reflows.js]
 [browser_toolbariconcolor_restyles.js]
 [browser_urlbar_keyed_search_reflows.js]
 skip-if = (os == 'linux') || (os == 'win' && debug) # Disabled on Linux and Windows debug due to perma failures. Bug 1392320.
 [browser_urlbar_search_reflows.js]
-skip-if = (os == 'linux') || (os == 'mac' && !debug) # Disabled on Linux and OS X opt due to frequent failures. Bug 1385932 and Bug 1384582
+skip-if = (os == 'linux') # Disabled on Linux and OS X opt due to frequent failures. Bug 1385932
 [browser_windowclose_reflows.js]
 [browser_windowopen_reflows.js]
 skip-if = os == 'linux' # Disabled due to frequent failures. Bug 1380465.

--- a/browser/base/content/test/performance/browser_tabstrip_overflow_underflow_reflows.js
+++ b/browser/base/content/test/performance/browser_tabstrip_overflow_underflow_reflows.js
@@ -41,17 +41,17 @@ add_task(async function() {
 
   await withReflowObserver(async function(dirtyFrame) {
     let switchDone = BrowserTestUtils.waitForEvent(window, "TabSwitchDone");
     BrowserOpenTab();
     await BrowserTestUtils.waitForEvent(gBrowser.selectedTab, "transitionend",
         false, e => e.propertyName === "max-width");
     await switchDone;
     await BrowserTestUtils.waitForCondition(() => {
-      return gBrowser.tabContainer.mTabstrip.hasAttribute("scrolledtoend");
+      return gBrowser.tabContainer.arrowScrollbox.hasAttribute("scrolledtoend");
     });
   }, EXPECTED_OVERFLOW_REFLOWS, window);
 
   await withReflowObserver(async function() {
     let switchDone = BrowserTestUtils.waitForEvent(window, "TabSwitchDone");
     let transitionPromise =
       BrowserTestUtils.waitForEvent(gBrowser.selectedTab,
                                     "transitionend", false,

--- a/browser/base/content/test/performance/browser_urlbar_search_reflows.js
+++ b/browser/base/content/test/performance/browser_urlbar_search_reflows.js
@@ -109,20 +109,20 @@ const EXPECTED_REFLOWS_SECOND_OPEN = [
       "_openAutocompletePopup@chrome://browser/content/urlbarBindings.xml",
       "openAutocompletePopup@chrome://browser/content/urlbarBindings.xml",
       "openPopup@chrome://global/content/bindings/autocomplete.xml",
       "set_popupOpen@chrome://global/content/bindings/autocomplete.xml",
     ],
   },
 ];
 
-const SEARCH_TERM = "urlbar-reflows";
+const SEARCH_TERM = "urlbar-reflows-" + Date.now();
 
 add_task(async function setup() {
-  await addDummyHistoryEntries();
+  await addDummyHistoryEntries(SEARCH_TERM);
 });
 
 /**
  * This test ensures that there are no unexpected
  * uninterruptible reflows when typing into the URL bar
  * with the default values in Places.
  */
 add_task(async function() {

--- a/browser/base/content/test/performance/head.js
+++ b/browser/base/content/test/performance/head.js
@@ -1,10 +1,12 @@
 "use strict";
 
+XPCOMUtils.defineLazyModuleGetter(this, "PlacesUtils",
+  "resource://gre/modules/PlacesUtils.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "PlacesTestUtils",
   "resource://testing-common/PlacesTestUtils.jsm");
 
 /**
  * Async utility function for ensuring that no unexpected uninterruptible
  * reflows occur during some period of time in a window.
  *
  * @param testFn (async function)
@@ -193,17 +195,17 @@ async function ensureNoPreloadedBrowser(
  *         tabstrip without causing it to overflow.
  */
 function computeMaxTabCount() {
   let currentTabCount = gBrowser.tabs.length;
   let newTabButton =
     document.getAnonymousElementByAttribute(gBrowser.tabContainer,
                                             "anonid", "tabs-newtab-button");
   let newTabRect = newTabButton.getBoundingClientRect();
-  let tabStripRect = gBrowser.tabContainer.mTabstrip.getBoundingClientRect();
+  let tabStripRect = gBrowser.tabContainer.arrowScrollbox.getBoundingClientRect();
   let availableTabStripWidth = tabStripRect.width - newTabRect.width;
 
   let tabMinWidth =
     parseInt(getComputedStyle(gBrowser.selectedTab, null).minWidth, 10);
 
   let maxTabCount = Math.floor(availableTabStripWidth / tabMinWidth) - currentTabCount;
   Assert.ok(maxTabCount > 0,
             "Tabstrip needs to be wide enough to accomodate at least 1 more tab " +
@@ -243,27 +245,30 @@ async function removeAllButFirstTab() {
   gBrowser.removeAllTabsBut(gBrowser.tabs[0]);
   await BrowserTestUtils.waitForCondition(() => gBrowser.tabs.length == 1);
   await SpecialPowers.popPrefEnv();
 }
 
 /**
  * Adds some entries to the Places database so that we can
  * do semi-realistic look-ups in the URL bar.
+ *
+ * @param searchStr (string)
+ *        Optional text to add to the search history items.
  */
-async function addDummyHistoryEntries() {
-  await PlacesTestUtils.clearHistory();
+async function addDummyHistoryEntries(searchStr = "") {
+  await PlacesUtils.history.clear();
   const NUM_VISITS = 10;
   let visits = [];
 
   for (let i = 0; i < NUM_VISITS; ++i) {
     visits.push({
       uri: `http://example.com/urlbar-reflows-${i}`,
-      title: `Reflow test for URL bar entry #${i}`,
+      title: `Reflow test for URL bar entry #${i} - ${searchStr}`,
     });
   }
 
   await PlacesTestUtils.addVisits(visits);
 
   registerCleanupFunction(async function() {
-    await PlacesTestUtils.clearHistory();
+    await PlacesUtils.history.clear();
   });
 }

--- a/browser/base/content/test/static/browser_misused_characters_in_strings.js
+++ b/browser/base/content/test/static/browser_misused_characters_in_strings.js
@@ -143,16 +143,20 @@ let gWhitelist = [{
   }, {
     file: "aboutNetworking.dtd",
     key: "aboutNetworking.logTutorial",
     type: "single-quote"
   }, {
     file: "preferences.properties",
     key: "searchResults.needHelp2",
     type: "double-quote"
+  }, {
+    file: "aboutdevtools.dtd",
+    key: "aboutDevtools.newsletter.privacy.label",
+    type: "single-quote"
   }
 ];
 
 /**
  * Check if an error should be ignored due to matching one of the whitelist
  * objects defined in gWhitelist.
  *
  * @param filepath The URI spec of the locale file

--- a/browser/base/content/test/tabs/browser_overflowScroll.js
+++ b/browser/base/content/test/tabs/browser_overflowScroll.js
@@ -2,56 +2,56 @@
 
 requestLongerTimeout(2);
 
 /**
  * Tests that scrolling the tab strip via the scroll buttons scrolls the right
  * amount in non-smoothscroll mode.
  */
 add_task(async function() {
-  let tabstrip = gBrowser.tabContainer.mTabstrip;
-  let scrollbox = tabstrip._scrollbox;
-  let originalSmoothScroll = tabstrip.smoothScroll;
+  let arrowScrollbox = gBrowser.tabContainer.arrowScrollbox;
+  let scrollbox = arrowScrollbox._scrollbox;
+  let originalSmoothScroll = arrowScrollbox.smoothScroll;
   let tabs = gBrowser.tabs;
   let tabMinWidth = parseInt(getComputedStyle(gBrowser.selectedTab, null).minWidth);
 
   let rect = ele => ele.getBoundingClientRect();
   let width = ele => rect(ele).width;
 
-  let tabCountForOverflow = Math.ceil(width(tabstrip) / tabMinWidth * 3);
+  let tabCountForOverflow = Math.ceil(width(arrowScrollbox) / tabMinWidth * 3);
 
   let left = ele => rect(ele).left;
   let right = ele => rect(ele).right;
   let isLeft = (ele, msg) => is(left(ele), left(scrollbox), msg);
   let isRight = (ele, msg) => is(right(ele), right(scrollbox), msg);
-  let elementFromPoint = x => tabstrip._elementFromPoint(x);
+  let elementFromPoint = x => arrowScrollbox._elementFromPoint(x);
   let nextLeftElement = () => elementFromPoint(left(scrollbox) - 1);
   let nextRightElement = () => elementFromPoint(right(scrollbox) + 1);
   let firstScrollable = () => tabs[gBrowser._numPinnedTabs];
 
-  tabstrip.smoothScroll = false;
+  arrowScrollbox.smoothScroll = false;
   registerCleanupFunction(() => {
-    tabstrip.smoothScroll = originalSmoothScroll;
+    arrowScrollbox.smoothScroll = originalSmoothScroll;
   });
 
   while (tabs.length < tabCountForOverflow) {
     BrowserTestUtils.addTab(gBrowser, "about:blank", { skipAnimation: true });
   }
 
   gBrowser.pinTab(tabs[0]);
 
   await BrowserTestUtils.waitForCondition(() => {
     return Array.from(gBrowser.tabs).every(tab => tab._fullyOpen);
   });
 
   ok(!scrollbox.hasAttribute("notoverflowing"),
      "Tab strip should be overflowing");
 
-  let upButton = tabstrip._scrollButtonUp;
-  let downButton = tabstrip._scrollButtonDown;
+  let upButton = arrowScrollbox._scrollButtonUp;
+  let downButton = arrowScrollbox._scrollButtonDown;
   let element;
 
   gBrowser.selectedTab = firstScrollable();
   ok(left(scrollbox) <= left(firstScrollable()), "Selecting the first tab scrolls it into view " +
      "(" + left(scrollbox) + " <= " + left(firstScrollable()) + ")");
 
   element = nextRightElement();
   EventUtils.synthesizeMouseAtCenter(downButton, {});

--- a/browser/components/extensions/ext-sidebarAction.js
+++ b/browser/components/extensions/ext-sidebarAction.js
@@ -136,26 +136,16 @@ this.sidebarAction = class extends Exten
     let install = this.extension.startupReason === "ADDON_INSTALL";
     for (let window of windowTracker.browserWindows()) {
       this.updateWindow(window);
       let {SidebarUI} = window;
       if (install || SidebarUI.lastOpenedId == this.id) {
         SidebarUI.show(this.id);
       }
     }
-
-    if (install && !Services.prefs.prefHasUserValue("extensions.sidebar-button.shown")) {
-      Services.prefs.setBoolPref("extensions.sidebar-button.shown", true);
-      // If the sidebar button has never been moved to the toolbar, move it now
-      // so the user can see/access the sidebars.
-      let widget = CustomizableUI.getWidget("sidebar-button");
-      if (!widget.areaType) {
-        CustomizableUI.addWidgetToArea("sidebar-button", CustomizableUI.AREA_NAVBAR, 0);
-      }
-    }
   }
 
   sidebarUrl(panel) {
     let url = `${sidebarURL}?panel=${encodeURIComponent(panel)}`;
 
     if (this.extension.remote) {
       url += "&remote=1";
     }

--- a/browser/components/extensions/test/browser/browser_ext_sidebarAction.js
+++ b/browser/components/extensions/test/browser/browser_ext_sidebarAction.js
@@ -46,37 +46,29 @@ let extData = {
 
 add_task(async function sidebar_initial_install() {
   ok(document.getElementById("sidebar-box").hidden, "sidebar box is not visible");
   let extension = ExtensionTestUtils.loadExtension(extData);
   await extension.startup();
   // Test sidebar is opened on install
   await extension.awaitMessage("sidebar");
   ok(!document.getElementById("sidebar-box").hidden, "sidebar box is visible");
-  // Test toolbar button is available
-  ok(document.getElementById("sidebar-button"), "sidebar button is in UI");
 
   await extension.unload();
   // Test that the sidebar was closed on unload.
   ok(document.getElementById("sidebar-box").hidden, "sidebar box is not visible");
-
-  // Move toolbar button back to customization.
-  CustomizableUI.removeWidgetFromArea("sidebar-button", CustomizableUI.AREA_NAVBAR);
-  ok(!document.getElementById("sidebar-button"), "sidebar button is not in UI");
 });
 
 
 add_task(async function sidebar_two_sidebar_addons() {
   let extension2 = ExtensionTestUtils.loadExtension(extData);
   await extension2.startup();
   // Test sidebar is opened on install
   await extension2.awaitMessage("sidebar");
   ok(!document.getElementById("sidebar-box").hidden, "sidebar box is visible");
-  // Test toolbar button is NOT available after first install
-  ok(!document.getElementById("sidebar-button"), "sidebar button is not in UI");
 
   // Test second sidebar install opens new sidebar
   let extension3 = ExtensionTestUtils.loadExtension(extData);
   await extension3.startup();
   // Test sidebar is opened on install
   await extension3.awaitMessage("sidebar");
   ok(!document.getElementById("sidebar-box").hidden, "sidebar box is visible");
   await extension3.unload();
@@ -92,13 +84,8 @@ add_task(async function sidebar_empty_pa
   await extension.startup();
   // Test sidebar is opened on install
   await extension.awaitMessage("sidebar");
   ok(!document.getElementById("sidebar-box").hidden, "sidebar box is visible in first window");
   extension.sendMessage("set-panel");
   await extension.awaitFinish();
   await extension.unload();
 });
-
-add_task(async function cleanup() {
-  // This is set on initial sidebar install.
-  Services.prefs.clearUserPref("extensions.sidebar-button.shown");
-});

--- a/browser/components/migration/MigrationUtils.jsm
+++ b/browser/components/migration/MigrationUtils.jsm
@@ -30,16 +30,18 @@ XPCOMUtils.defineLazyModuleGetter(this, 
 XPCOMUtils.defineLazyModuleGetter(this, "ResponsivenessMonitor",
                                   "resource://gre/modules/ResponsivenessMonitor.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Sqlite",
                                   "resource://gre/modules/Sqlite.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "TelemetryStopwatch",
                                   "resource://gre/modules/TelemetryStopwatch.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "WindowsRegistry",
                                   "resource://gre/modules/WindowsRegistry.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "setTimeout",
+                                  "resource://gre/modules/Timer.jsm");
 
 var gMigrators = null;
 var gProfileStartup = null;
 var gMigrationBundle = null;
 var gPreviousDefaultBrowserKey = "";
 
 let gKeepUndoData = false;
 let gUndoData = null;

new file mode 100644
--- /dev/null
+++ b/browser/components/migration/tests/unit/test_MigrationUtils_timedRetry.js
@@ -0,0 +1,26 @@
+"use strict";
+
+XPCOMUtils.defineLazyModuleGetter(this, "OS",
+                                  "resource://gre/modules/osfile.jsm");
+
+let tmpFile = FileUtils.getDir("TmpD", [], true);
+let dbConn;
+
+add_task(async function setup() {
+  tmpFile.append("TestDB");
+  dbConn = await Sqlite.openConnection({ path: tmpFile.path });
+
+  do_register_cleanup(() => {
+    dbConn.close();
+    OS.File.remove(tmpFile.path);
+  });
+});
+
+add_task(async function testgetRowsFromDBWithoutLocksRetries() {
+  let promise = MigrationUtils.getRowsFromDBWithoutLocks(tmpFile.path,
+                                                         "Temp DB",
+                                                         "SELECT * FROM moz_temp_table");
+  await new Promise(resolve => do_timeout(50, resolve));
+  dbConn.execute("CREATE TABLE moz_temp_table (id INTEGER PRIMARY KEY)");
+  await promise;
+});

--- a/browser/components/migration/tests/unit/xpcshell.ini
+++ b/browser/components/migration/tests/unit/xpcshell.ini
@@ -18,10 +18,11 @@ skip-if = os != "win"
 skip-if = os != "win"
 [test_fx_telemetry.js]
 [test_IE_bookmarks.js]
 skip-if = !(os == "win" && bits == 64) # bug 1392396
 [test_IE_cookies.js]
 skip-if = os != "win"
 [test_IE7_passwords.js]
 skip-if = os != "win"
+[test_MigrationUtils_timedRetry.js]
 [test_Safari_bookmarks.js]
 skip-if = os != "mac"

--- a/browser/components/places/tests/browser/browser_library_left_pane_middleclick.js
+++ b/browser/components/places/tests/browser/browser_library_left_pane_middleclick.js
@@ -2,190 +2,86 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
  /**
  * Tests middle-clicking items in the Library.
  */
 
-const ENABLE_HISTORY_PREF = "places.history.enabled";
+const URIs = ["about:license", "about:"];
 
 var gLibrary = null;
-var gTests = [];
-var gCurrentTest = null;
 
-// Listener for TabOpen and tabs progress.
-var gTabsListener = {
-  _loadedURIs: [],
-  _openTabsCount: 0,
-
-  handleEvent(aEvent) {
-    if (aEvent.type != "TabOpen")
-      return;
-
-    if (++this._openTabsCount == gCurrentTest.URIs.length) {
-      is(gBrowser.tabs.length, gCurrentTest.URIs.length + 1,
-         "We have opened " + gCurrentTest.URIs.length + " new tab(s)");
-    }
-
-    var tab = aEvent.target;
-    is(tab.ownerGlobal, window,
-       "Tab has been opened in current browser window");
-  },
-
-  onLocationChange(aBrowser, aWebProgress, aRequest, aLocationURI,
-                             aFlags) {
-    var spec = aLocationURI.spec;
-    ok(true, spec);
-    // When a new tab is opened, location is first set to "about:blank", so
-    // we can ignore those calls.
-    // Ignore multiple notifications for the same URI too.
-    if (spec == "about:blank" || this._loadedURIs.includes(spec))
-      return;
-
-    ok(gCurrentTest.URIs.includes(spec),
-       "Opened URI found in list: " + spec);
-
-    if (gCurrentTest.URIs.includes(spec))
-      this._loadedURIs.push(spec);
-
-    if (this._loadedURIs.length == gCurrentTest.URIs.length) {
-      // We have correctly opened all URIs.
-
-      // Reset arrays.
-      this._loadedURIs.length = 0;
-
-      this._openTabsCount = 0;
-
-      executeSoon(function() {
-        // Close all tabs.
-        while (gBrowser.tabs.length > 1)
-          gBrowser.removeCurrentTab();
-
-        // Test finished.  This will move to the next one.
-        waitForFocus(gCurrentTest.finish, gBrowser.ownerGlobal);
-      });
-    }
-  }
-};
-
-// ------------------------------------------------------------------------------
-// Open a folder in tabs.
-
-gTests.push({
-  desc: "Open a folder in tabs.",
-  URIs: ["about:buildconfig", "about:"],
-  _folderId: -1,
-
-  setup() {
-    var bs = PlacesUtils.bookmarks;
-    // Create a new folder.
-    var folderId = bs.createFolder(bs.unfiledBookmarksFolder,
-                                   "Folder",
-                                   bs.DEFAULT_INDEX);
-    this._folderId = folderId;
-
-    // Add bookmarks in folder.
-    this.URIs.forEach(function(aURI) {
-      bs.insertBookmark(folderId,
-                        PlacesUtils._uri(aURI),
-                        bs.DEFAULT_INDEX,
-                        "Title");
-    });
-
-    // Select unsorted bookmarks root in the left pane.
-    gLibrary.PlacesOrganizer.selectLeftPaneQuery("UnfiledBookmarks");
-    isnot(gLibrary.PlacesOrganizer._places.selectedNode, null,
-          "We correctly have selection in the Library left pane");
-    // Get our bookmark in the right pane.
-    var folderNode = gLibrary.ContentTree.view.view.nodeForTreeIndex(0);
-    is(folderNode.title, "Folder", "Found folder in the right pane");
-  },
-
-  finish() {
-    setTimeout(runNextTest, 0);
-  },
-
-  cleanup() {
-    PlacesUtils.bookmarks.removeItem(this._folderId);
-  }
-});
-
-// ------------------------------------------------------------------------------
-
-function test() {
-  waitForExplicitFinish();
-
-  // Sanity checks.
-  ok(PlacesUtils, "PlacesUtils in context");
-  ok(PlacesUIUtils, "PlacesUIUtils in context");
-
-  // Add tabs listeners.
-  gBrowser.tabContainer.addEventListener("TabOpen", gTabsListener);
-  gBrowser.addTabsProgressListener(gTabsListener);
-
+add_task(async function test_setup() {
   // Temporary disable history, so we won't record pages navigation.
-  gPrefService.setBoolPref(ENABLE_HISTORY_PREF, false);
+  await SpecialPowers.pushPrefEnv({set: [
+    ["places.history.enabled", false]
+  ]});
 
   // Open Library window.
-  openLibrary(function(library) {
-    gLibrary = library;
-    // Kick off tests.
-    runNextTest();
-  });
-}
-
-function runNextTest() {
-  // Cleanup from previous test.
-  if (gCurrentTest)
-    gCurrentTest.cleanup();
+  gLibrary = await promiseLibrary();
 
-  if (gTests.length > 0) {
-    // Goto next test.
-    gCurrentTest = gTests.shift();
-    info("Start of test: " + gCurrentTest.desc);
-    // Test setup will set Library so that the bookmark to be opened is the
-    // first node in the content (right pane) tree.
-    gCurrentTest.setup();
-
-    gLibrary.focus();
-    waitForFocus(function() {
-      // Open the "Other Bookmarks" folder.
-      gLibrary.PlacesOrganizer.selectLeftPaneQuery("UnfiledBookmarks");
-      gLibrary.PlacesOrganizer._places.selectedNode.containerOpen = true;
-      // Now middle-click on the bookmark contained with it.
-      let bookmarkedNode = gLibrary.PlacesOrganizer._places.selectedNode.getChild(0);
-      mouseEventOnCell(gLibrary.PlacesOrganizer._places,
-        gLibrary.PlacesOrganizer._places.view.treeIndexForNode(bookmarkedNode),
-        0,
-        { button: 1 });
-    }, gLibrary);
-  } else {
-    // No more tests.
-
+  registerCleanupFunction(async () => {
     // We must close "Other Bookmarks" ready for other tests.
     gLibrary.PlacesOrganizer.selectLeftPaneQuery("UnfiledBookmarks");
     gLibrary.PlacesOrganizer._places.selectedNode.containerOpen = false;
 
+    await PlacesUtils.bookmarks.eraseEverything();
+
     // Close Library window.
-    gLibrary.close();
+    await promiseLibraryClosed(gLibrary);
+  });
+});
 
-    // Remove tabs listeners.
-    gBrowser.tabContainer.removeEventListener("TabOpen", gTabsListener);
-    gBrowser.removeTabsProgressListener(gTabsListener);
+add_task(async function test_open_folder_in_tabs() {
+  let children = URIs.map(url => {
+    return {
+      title: "Title",
+      url
+    }
+  });
+
+  // Create a new folder.
+  await PlacesUtils.bookmarks.insertTree({
+    guid: PlacesUtils.bookmarks.unfiledGuid,
+    children: [{
+      title: "Folder",
+      type: PlacesUtils.bookmarks.TYPE_FOLDER,
+      children,
+    }],
+  });
 
-    // Restore history.
-    try {
-      gPrefService.clearUserPref(ENABLE_HISTORY_PREF);
-    } catch (ex) {}
+  // Select unsorted bookmarks root in the left pane.
+  gLibrary.PlacesOrganizer.selectLeftPaneQuery("UnfiledBookmarks");
+  Assert.notEqual(gLibrary.PlacesOrganizer._places.selectedNode, null,
+        "We correctly have selection in the Library left pane");
+
+  // Get our bookmark in the right pane.
+  var folderNode = gLibrary.ContentTree.view.view.nodeForTreeIndex(0);
+  Assert.equal(folderNode.title, "Folder", "Found folder in the right pane");
+
+  gLibrary.PlacesOrganizer._places.selectedNode.containerOpen = true;
 
-    finish();
-  }
-}
+  // Now middle-click on the bookmark contained with it.
+  let promiseLoaded = Promise.all(URIs.map(uri =>
+    BrowserTestUtils.waitForNewTab(gBrowser, uri, false, true)));
+
+  let bookmarkedNode = gLibrary.PlacesOrganizer._places.selectedNode.getChild(0);
+  mouseEventOnCell(gLibrary.PlacesOrganizer._places,
+    gLibrary.PlacesOrganizer._places.view.treeIndexForNode(bookmarkedNode),
+    0,
+    { button: 1 });
+
+  let tabs = await promiseLoaded;
+
+  Assert.ok(true, "Expected tabs were loaded");
+
+  await Promise.all(tabs.map(tab => BrowserTestUtils.removeTab(tab)));
+});
 
 function mouseEventOnCell(aTree, aRowIndex, aColumnIndex, aEventDetails) {
   var selection = aTree.view.selection;
   selection.select(aRowIndex);
   aTree.treeBoxObject.ensureRowIsVisible(aRowIndex);
   var column = aTree.columns[aColumnIndex];
 
   // get cell coordinates

--- a/browser/components/places/tests/browser/browser_library_middleclick.js
+++ b/browser/components/places/tests/browser/browser_library_middleclick.js
@@ -2,272 +2,205 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
  /**
  * Tests middle-clicking items in the Library.
  */
 
-const ENABLE_HISTORY_PREF = "places.history.enabled";
+const URIs = ["about:license", "about:"];
 
 var gLibrary = null;
 var gTests = [];
-var gCurrentTest = null;
 
-// Listener for TabOpen and tabs progress.
-var gTabsListener = {
-  _loadedURIs: [],
-  _openTabsCount: 0,
+add_task(async function test_setup() {
+  // Increase timeout, this test can be quite slow due to waitForFocus calls.
+  requestLongerTimeout(2);
 
-  handleEvent(aEvent) {
-    if (aEvent.type != "TabOpen")
-      return;
+  // Temporary disable history, so we won't record pages navigation.
+  await SpecialPowers.pushPrefEnv({set: [
+    ["places.history.enabled", false]
+  ]});
 
-    if (++this._openTabsCount == gCurrentTest.URIs.length) {
-      is(gBrowser.tabs.length, gCurrentTest.URIs.length + 1,
-         "We have opened " + gCurrentTest.URIs.length + " new tab(s)");
-    }
-
-    var tab = aEvent.target;
-    is(tab.ownerGlobal, window,
-       "Tab has been opened in current browser window");
-  },
+  // Ensure the database is empty.
+  await PlacesUtils.bookmarks.eraseEverything();
 
-  onLocationChange(aBrowser, aWebProgress, aRequest, aLocationURI,
-                             aFlags) {
-    var spec = aLocationURI.spec;
-    ok(true, spec);
-    // When a new tab is opened, location is first set to "about:blank", so
-    // we can ignore those calls.
-    // Ignore multiple notifications for the same URI too.
-    if (spec == "about:blank" || this._loadedURIs.includes(spec))
-      return;
-
-    ok(gCurrentTest.URIs.includes(spec),
-       "Opened URI found in list: " + spec);
-
-    if (gCurrentTest.URIs.includes(spec))
-      this._loadedURIs.push(spec);
-
-    if (this._loadedURIs.length == gCurrentTest.URIs.length) {
-      // We have correctly opened all URIs.
+  // Open Library window.
+  gLibrary = await promiseLibrary();
 
-      // Reset arrays.
-      this._loadedURIs.length = 0;
-
-      this._openTabsCount = 0;
-
-      executeSoon(function() {
-        // Close all tabs.
-        while (gBrowser.tabs.length > 1)
-          gBrowser.removeCurrentTab();
+  registerCleanupFunction(async () => {
+    // We must close "Other Bookmarks" ready for other tests.
+    gLibrary.PlacesOrganizer.selectLeftPaneQuery("UnfiledBookmarks");
+    gLibrary.PlacesOrganizer._places.selectedNode.containerOpen = false;
 
-        // Test finished.  This will move to the next one.
-        waitForFocus(gCurrentTest.finish, gBrowser.ownerGlobal);
-      });
-    }
-  }
-};
+    await PlacesUtils.bookmarks.eraseEverything();
 
-// ------------------------------------------------------------------------------
-// Open bookmark in a new tab.
+    // Close Library window.
+    await promiseLibraryClosed(gLibrary);
+  });
+});
 
 gTests.push({
   desc: "Open bookmark in a new tab.",
   URIs: ["about:buildconfig"],
-  _itemId: -1,
+  _bookmark: null,
 
-  setup() {
-    var bs = PlacesUtils.bookmarks;
+  async setup() {
     // Add a new unsorted bookmark.
-    this._itemId = bs.insertBookmark(bs.unfiledBookmarksFolder,
-                                     PlacesUtils._uri(this.URIs[0]),
-                                     bs.DEFAULT_INDEX,
-                                     "Title");
+    this._bookmark = await PlacesUtils.bookmarks.insert({
+      parentGuid: PlacesUtils.bookmarks.unfiledGuid,
+      title: "Title",
+      url: this.URIs[0],
+    });
+
     // Select unsorted bookmarks root in the left pane.
     gLibrary.PlacesOrganizer.selectLeftPaneQuery("UnfiledBookmarks");
-    isnot(gLibrary.PlacesOrganizer._places.selectedNode, null,
-          "We correctly have selection in the Library left pane");
+    Assert.notEqual(gLibrary.PlacesOrganizer._places.selectedNode, null,
+      "We correctly have selection in the Library left pane");
+
     // Get our bookmark in the right pane.
     var bookmarkNode = gLibrary.ContentTree.view.view.nodeForTreeIndex(0);
-    is(bookmarkNode.uri, this.URIs[0], "Found bookmark in the right pane");
+    Assert.equal(bookmarkNode.uri, this.URIs[0], "Found bookmark in the right pane");
   },
 
-  finish() {
-    setTimeout(runNextTest, 0);
-  },
-
-  cleanup() {
-    PlacesUtils.bookmarks.removeItem(this._itemId);
+  async cleanup() {
+    await PlacesUtils.bookmarks.remove(this._bookmark);
   }
 });
 
 // ------------------------------------------------------------------------------
 // Open a folder in tabs.
-
+//
 gTests.push({
   desc: "Open a folder in tabs.",
   URIs: ["about:buildconfig", "about:"],
-  _folderId: -1,
+  _bookmarks: null,
 
-  setup() {
-    var bs = PlacesUtils.bookmarks;
+  async setup() {
     // Create a new folder.
-    var folderId = bs.createFolder(bs.unfiledBookmarksFolder,
-                                   "Folder",
-                                   bs.DEFAULT_INDEX);
-    this._folderId = folderId;
+    let children = this.URIs.map(url => {
+      return {
+        title: "Title",
+        url,
+      }
+    });
 
-    // Add bookmarks in folder.
-    this.URIs.forEach(function(aURI) {
-      bs.insertBookmark(folderId,
-                        PlacesUtils._uri(aURI),
-                        bs.DEFAULT_INDEX,
-                        "Title");
+    this._bookmarks = await PlacesUtils.bookmarks.insertTree({
+      guid: PlacesUtils.bookmarks.unfiledGuid,
+      children: [{
+        title: "Folder",
+        type: PlacesUtils.bookmarks.TYPE_FOLDER,
+        children,
+      }],
     });
 
     // Select unsorted bookmarks root in the left pane.
     gLibrary.PlacesOrganizer.selectLeftPaneQuery("UnfiledBookmarks");
     isnot(gLibrary.PlacesOrganizer._places.selectedNode, null,
           "We correctly have selection in the Library left pane");
     // Get our bookmark in the right pane.
     var folderNode = gLibrary.ContentTree.view.view.nodeForTreeIndex(0);
     is(folderNode.title, "Folder", "Found folder in the right pane");
   },
 
-  finish() {
-    setTimeout(runNextTest, 0);
-  },
-
-  cleanup() {
-    PlacesUtils.bookmarks.removeItem(this._folderId);
+  async cleanup() {
+    await PlacesUtils.bookmarks.remove(this._bookmarks[0]);
   }
 });
 
 // ------------------------------------------------------------------------------
 // Open a query in tabs.
 
 gTests.push({
   desc: "Open a query in tabs.",
   URIs: ["about:buildconfig", "about:"],
-  _folderId: -1,
-  _queryId: -1,
+  _bookmarks: null,
+  _query: null,
 
-  setup() {
-    var bs = PlacesUtils.bookmarks;
-    // Create a new folder.
-    var folderId = bs.createFolder(bs.unfiledBookmarksFolder,
-                                   "Folder",
-                                   bs.DEFAULT_INDEX);
-    this._folderId = folderId;
+  async setup() {
+    let children = this.URIs.map(url => {
+      return {
+        title: "Title",
+        url,
+      }
+    });
 
-    // Add bookmarks in folder.
-    this.URIs.forEach(function(aURI) {
-      bs.insertBookmark(folderId,
-                        PlacesUtils._uri(aURI),
-                        bs.DEFAULT_INDEX,
-                        "Title");
+    this._bookmarks = await PlacesUtils.bookmarks.insertTree({
+      guid: PlacesUtils.bookmarks.unfiledGuid,
+      children: [{
+        title: "Folder",
+        type: PlacesUtils.bookmarks.TYPE_FOLDER,
+        children,
+      }],
     });
 
     // Create a bookmarks query containing our bookmarks.
     var hs = PlacesUtils.history;
     var options = hs.getNewQueryOptions();
     options.queryType = Ci.nsINavHistoryQueryOptions.QUERY_TYPE_BOOKMARKS;
     var query = hs.getNewQuery();
     // The colon included in the terms selects only about: URIs. If not included
     // we also may get pages like about.html included in the query result.
     query.searchTerms = "about:";
     var queryString = hs.queriesToQueryString([query], 1, options);
-    this._queryId = bs.insertBookmark(bs.unfiledBookmarksFolder,
-                                     PlacesUtils._uri(queryString),
-                                     0, // It must be the first.
-                                     "Query");
+    this._query = await PlacesUtils.bookmarks.insert({
+      index: 0, // it must be the first
+      parentGuid: PlacesUtils.bookmarks.unfiledGuid,
+      title: "Query",
+      url: queryString,
+    });
+
+    gLibrary.PlacesOrganizer.selectLeftPaneQuery("Query");
 
     // Select unsorted bookmarks root in the left pane.
     gLibrary.PlacesOrganizer.selectLeftPaneQuery("UnfiledBookmarks");
     isnot(gLibrary.PlacesOrganizer._places.selectedNode, null,
           "We correctly have selection in the Library left pane");
     // Get our bookmark in the right pane.
     var folderNode = gLibrary.ContentTree.view.view.nodeForTreeIndex(0);
     is(folderNode.title, "Query", "Found query in the right pane");
   },
 
-  finish() {
-    setTimeout(runNextTest, 0);
-  },
-
-  cleanup() {
-    PlacesUtils.bookmarks.removeItem(this._folderId);
-    PlacesUtils.bookmarks.removeItem(this._queryId);
+  async cleanup() {
+    await PlacesUtils.bookmarks.remove(this._bookmarks[0]);
+    await PlacesUtils.bookmarks.remove(this._query);
   }
 });
 
-// ------------------------------------------------------------------------------
+async function runTest(test) {
+  info("Start of test: " + test.desc);
+  // Test setup will set Library so that the bookmark to be opened is the
+  // first node in the content (right pane) tree.
+  await test.setup();
 
-function test() {
-  waitForExplicitFinish();
-  // Increase timeout, this test can be quite slow due to waitForFocus calls.
-  requestLongerTimeout(2);
-
-  // Sanity checks.
-  ok(PlacesUtils, "PlacesUtils in context");
-  ok(PlacesUIUtils, "PlacesUIUtils in context");
+  // Middle click on first node in the content tree of the Library.
+  gLibrary.focus();
+  await SimpleTest.promiseFocus(gLibrary);
 
-  // Add tabs listeners.
-  gBrowser.tabContainer.addEventListener("TabOpen", gTabsListener);
-  gBrowser.addTabsProgressListener(gTabsListener);
+  // Now middle-click on the bookmark contained with it.
+  let promiseLoaded = Promise.all(test.URIs.map(uri =>
+    BrowserTestUtils.waitForNewTab(gBrowser, uri, false, true)));
 
-  // Temporary disable history, so we won't record pages navigation.
-  gPrefService.setBoolPref(ENABLE_HISTORY_PREF, false);
+  mouseEventOnCell(gLibrary.ContentTree.view, 0, 0, { button: 1 });
 
-  // Open Library window.
-  openLibrary(function(library) {
-    gLibrary = library;
-    // Kick off tests.
-    runNextTest();
-  });
+  let tabs = await promiseLoaded;
+
+  Assert.ok(true, "Expected tabs were loaded");
+
+  await Promise.all(tabs.map(tab => BrowserTestUtils.removeTab(tab)));
+
+  await test.cleanup();
 }
 
-function runNextTest() {
-  // Cleanup from previous test.
-  if (gCurrentTest)
-    gCurrentTest.cleanup();
-
-  if (gTests.length > 0) {
-    // Goto next test.
-    gCurrentTest = gTests.shift();
-    info("Start of test: " + gCurrentTest.desc);
-    // Test setup will set Library so that the bookmark to be opened is the
-    // first node in the content (right pane) tree.
-    gCurrentTest.setup();
-
-    // Middle click on first node in the content tree of the Library.
-    gLibrary.focus();
-    waitForFocus(function() {
-      mouseEventOnCell(gLibrary.ContentTree.view, 0, 0, { button: 1 });
-    }, gLibrary);
-  } else {
-    // No more tests.
-
-    // Close Library window.
-    gLibrary.close();
-
-    // Remove tabs listeners.
-    gBrowser.tabContainer.removeEventListener("TabOpen", gTabsListener);
-    gBrowser.removeTabsProgressListener(gTabsListener);
-
-    // Restore history.
-    try {
-      gPrefService.clearUserPref(ENABLE_HISTORY_PREF);
-    } catch (ex) {}
-
-    finish();
+add_task(async function test_all() {
+  for (let test of gTests) {
+    await runTest(test);
   }
-}
+});
 
 function mouseEventOnCell(aTree, aRowIndex, aColumnIndex, aEventDetails) {
   var selection = aTree.view.selection;
   selection.select(aRowIndex);
   aTree.treeBoxObject.ensureRowIsVisible(aRowIndex);
   var column = aTree.columns[aColumnIndex];
 
   // get cell coordinates

--- a/browser/components/sessionstore/SessionStore.jsm
+++ b/browser/components/sessionstore/SessionStore.jsm
@@ -3345,19 +3345,19 @@ var SessionStoreInternal = {
       selectTab = Math.min(selectTab, winData.tabs.length);
     }
 
     let tabbrowser = aWindow.gBrowser;
     let newTabCount = winData.tabs.length;
     var tabs = [];
 
     // disable smooth scrolling while adding, moving, removing and selecting tabs
-    let tabstrip = tabbrowser.tabContainer.mTabstrip;
-    let smoothScroll = tabstrip.smoothScroll;
-    tabstrip.smoothScroll = false;
+    let arrowScrollbox = tabbrowser.tabContainer.arrowScrollbox;
+    let smoothScroll = arrowScrollbox.smoothScroll;
+    arrowScrollbox.smoothScroll = false;
 
     // We need to keep track of the initially open tabs so that they
     // can be moved to the end of the restored tabs.
     let initialTabs;
     if (!overwriteTabs && firstWindow) {
       initialTabs = Array.slice(tabbrowser.tabs);
     }
 
@@ -3489,17 +3489,17 @@ var SessionStoreInternal = {
     }
 
     // Restore tabs, if any.
     if (winData.tabs.length) {
       this.restoreTabs(aWindow, tabs, winData.tabs, selectTab);
     }
 
     // set smoothScroll back to the original value
-    tabstrip.smoothScroll = smoothScroll;
+    arrowScrollbox.smoothScroll = smoothScroll;
 
     TelemetryStopwatch.finish("FX_SESSION_RESTORE_RESTORE_WINDOW_MS");
     if (Services.prefs.getIntPref("browser.tabs.restorebutton") != 0 ) {
       Services.telemetry.scalarAdd("browser.session.restore.number_of_tabs", winData.tabs.length);
       Services.telemetry.scalarAdd("browser.session.restore.number_of_win", 1);
     }
 
     this._setWindowStateReady(aWindow);

--- a/browser/config/mozconfigs/win32/mingw32
+++ b/browser/config/mozconfigs/win32/mingw32
@@ -3,20 +3,16 @@
 #    SOCORRO_SYMBOL_UPLOAD_TOKEN_FILE - shouldn't be used?
 #    TOOLTOOL_DIR
 #    MAKECAB - shouldn't be used?
 . "$topsrcdir/build/mozconfig.win-common"
 
 # MinGW does not have (or need) makecab
 unset MAKECAB
 
-# These aren't supported on mingw at this time
-# Bug 1393817
-MOZ_AUTOMATION_L10N_CHECK=0
-
 # Sets:
 #  build/mozconfig.common
 #    AUTOCLOBBER=1
 #    --enable-crashreporter
 #    --enable-release
 #    LLVM_CONFIG
 #    MOZ_ADDON_SIGNING
 #    MOZ_REQUIRE_SIGNING

--- a/browser/confvars.sh
+++ b/browser/confvars.sh
@@ -23,20 +23,16 @@ if test "$OS_ARCH" = "WINNT"; then
             "$MOZ_UPDATE_CHANNEL" = "release"; then
       if ! test "$MOZ_DEBUG"; then
         MOZ_STUB_INSTALLER=1
       fi
     fi
   fi
 fi
 
-if test "$NIGHTLY_BUILD"; then
-  MOZ_RUST_URLPARSE=1
-fi
-
 # Enable building ./signmar and running libmar signature tests
 MOZ_ENABLE_SIGNMAR=1
 
 MOZ_APP_VERSION=$FIREFOX_VERSION
 MOZ_APP_VERSION_DISPLAY=$FIREFOX_VERSION_DISPLAY
 # MOZ_APP_DISPLAYNAME will be set by branding/configure.sh
 # MOZ_BRANDING_DIRECTORY is the default branding directory used when none is
 # specified. It should never point to the "official" branding directory.

--- a/browser/extensions/formautofill/FormAutofillUtils.jsm
+++ b/browser/extensions/formautofill/FormAutofillUtils.jsm
@@ -234,16 +234,64 @@ this.FormAutofillUtils = {
       let dataset = this.getCountryAddressData(country);
       let languages = dataset.languages ? dataset.languages.split("~") : [dataset.lang];
       this._collators[country] = languages.map(lang => new Intl.Collator(lang, {sensitivity: "base", ignorePunctuation: true}));
     }
     return this._collators[country];
   },
 
   /**
+   * Parse a country address format string and outputs an array of fields.
+   * Spaces, commas, and other literals are ignored in this implementation.
+   * For example, format string "%A%n%C, %S" should return:
+   * [
+   *   {fieldId: "street-address", newLine: true},
+   *   {fieldId: "address-level2"},
+   *   {fieldId: "address-level1"},
+   * ]
+   *
+   * @param   {string} fmt Country address format string
+   * @returns {array<object>} List of fields
+   */
+  parseAddressFormat(fmt) {
+    if (!fmt) {
+      throw new Error("fmt string is missing.");
+    }
+    // Based on the list of fields abbreviations in
+    // https://github.com/googlei18n/libaddressinput/wiki/AddressValidationMetadata
+    const fieldsLookup = {
+      N: "name",
+      O: "organization",
+      A: "street-address",
+      S: "address-level1",
+      C: "address-level2",
+      Z: "postal-code",
+      n: "newLine",
+    };
+
+    return fmt.match(/%[^%]/g).reduce((parsed, part) => {
+      // Take the first letter of each segment and try to identify it
+      let fieldId = fieldsLookup[part[1]];
+      // Early return if cannot identify part.
+      if (!fieldId) {
+        return parsed;
+      }
+      // If a new line is detected, add an attribute to the previous field.
+      if (fieldId == "newLine") {
+        let size = parsed.length;
+        if (size) {
+          parsed[size - 1].newLine = true;
+        }
+        return parsed;
+      }
+      return parsed.concat({fieldId});
+    }, []);
+  },
+
+  /**
    * Use alternative country name list to identify a country code from a
    * specified country name.
    * @param   {string} countryName A country name to be identified
    * @param   {string} [countrySpecified] A country code indicating that we only
    *                                      search its alternative names if specified.
    * @returns {string} The matching country code.
    */
   identifyCountryCode(countryName, countrySpecified) {

new file mode 100644
--- /dev/null
+++ b/browser/extensions/formautofill/test/unit/test_parseAddressFormat.js
@@ -0,0 +1,47 @@
+"use strict";
+
+Cu.import("resource://formautofill/FormAutofillUtils.jsm");
+
+add_task(async function test_parseAddressFormat() {
+  const TEST_CASES = [
+    {
+      fmt: "%N%n%O%n%A%n%C, %S %Z", // US
+      parsed: [
+        {fieldId: "name", newLine: true},
+        {fieldId: "organization", newLine: true},
+        {fieldId: "street-address", newLine: true},
+        {fieldId: "address-level2"},
+        {fieldId: "address-level1"},
+        {fieldId: "postal-code"},
+      ],
+    },
+    {
+      fmt: "%N%n%O%n%A%n%C %S %Z", // CA
+      parsed: [
+        {fieldId: "name", newLine: true},
+        {fieldId: "organization", newLine: true},
+        {fieldId: "street-address", newLine: true},
+        {fieldId: "address-level2"},
+        {fieldId: "address-level1"},
+        {fieldId: "postal-code"},
+      ],
+    },
+    {
+      fmt: "%N%n%O%n%A%n%Z %C", // DE
+      parsed: [
+        {fieldId: "name", newLine: true},
+        {fieldId: "organization", newLine: true},
+        {fieldId: "street-address", newLine: true},
+        {fieldId: "postal-code"},
+        {fieldId: "address-level2"},
+      ],
+    },
+  ];
+
+  Assert.throws(() => FormAutofillUtils.parseAddressFormat(),
+                /fmt string is missing./,
+                "Should throw if fmt is empty");
+  for (let tc of TEST_CASES) {
+    Assert.deepEqual(FormAutofillUtils.parseAddressFormat(tc.fmt), tc.parsed);
+  }
+});

--- a/browser/extensions/formautofill/test/unit/xpcshell.ini
+++ b/browser/extensions/formautofill/test/unit/xpcshell.ini
@@ -33,16 +33,17 @@ support-files =
 [test_isAvailable.js]
 [test_isCJKName.js]
 [test_isFieldEligibleForAutofill.js]
 [test_markAsAutofillField.js]
 [test_masterPassword.js]
 [test_migrateRecords.js]
 [test_nameUtils.js]
 [test_onFormSubmitted.js]
+[test_parseAddressFormat.js]
 [test_profileAutocompleteResult.js]
 [test_phoneNumber.js]
 [test_reconcile.js]
 [test_savedFieldNames.js]
 [test_toOneLineAddress.js]
 [test_storage_tombstones.js]
 [test_storage_syncfields.js]
 [test_transformFields.js]

--- a/devtools/shim/aboutdevtools/aboutdevtools.js
+++ b/devtools/shim/aboutdevtools/aboutdevtools.js
@@ -4,16 +4,22 @@
 
 "use strict";
 
 const { utils: Cu } = Components;
 const { Services } = Cu.import("resource://gre/modules/Services.jsm", {});
 
 const DEVTOOLS_ENABLED_PREF = "devtools.enabled";
 
+const TELEMETRY_OPENED_KEY = "DEVTOOLS_ABOUT_DEVTOOLS_OPENED_KEY";
+const TELEMETRY_OPENED_REASON = "DEVTOOLS_ABOUT_DEVTOOLS_OPENED_REASON";
+const TELEMETRY_OPENED = "devtools.aboutdevtools.opened";
+const TELEMETRY_INSTALLED = "devtools.aboutdevtools.installed";
+const TELEMETRY_NOINSTALL_EXITS = "devtools.aboutdevtools.noinstall_exits";
+
 const MESSAGES = {
   AboutDebugging: "about-debugging-message",
   ContextMenu: "inspect-element-message",
   HamburgerMenu: "menu-message",
   KeyShortcut: "key-shortcut-message",
   SystemMenu: "menu-message",
 };
 
@@ -22,25 +28,35 @@ const aboutDevtoolsBundle = Services.str
 
 const KEY_SHORTCUTS_STRINGS = "chrome://devtools-shim/locale/key-shortcuts.properties";
 const keyShortcutsBundle = Services.strings.createBundle(KEY_SHORTCUTS_STRINGS);
 
 // URL constructor doesn't support about: scheme,
 // we have to use http in order to have working searchParams.
 let url = new URL(window.location.href.replace("about:", "http://"));
 let reason = url.searchParams.get("reason");
+let keyid = url.searchParams.get("keyid");
 let tabid = parseInt(url.searchParams.get("tabid"), 10);
 
+// Keep track of the initial devtools.enabled value to track exits in telemetry.
+let isEnabledOnLoad;
+
 function getToolboxShortcut() {
   const modifier = Services.appinfo.OS == "Darwin" ? "Cmd+Opt+" : "Ctrl+Shift+";
   return modifier + keyShortcutsBundle.GetStringFromName("toggleToolbox.commandkey");
 }
 
 function onInstallButtonClick() {
   Services.prefs.setBoolPref("devtools.enabled", true);
+
+  try {
+    Services.telemetry.scalarAdd(TELEMETRY_INSTALLED, 1);
+  } catch (e) {
+    dump("about:devtools oninstall telemetry failed: " + e + "\n");
+  }
 }
 
 function onCloseButtonClick() {
   window.close();
 }
 
 function updatePage() {
   const installPage = document.getElementById("install-page");
@@ -135,18 +151,21 @@ function createFeatureEl(feature) {
      </p>`;
 
   return li;
 }
 
 window.addEventListener("load", function () {
   const inspectorShortcut = getToolboxShortcut();
   const welcomeMessage = document.getElementById("welcome-message");
-  welcomeMessage.textContent = welcomeMessage.textContent.replace(
-    "##INSPECTOR_SHORTCUT##", inspectorShortcut);
+
+  // Set the welcome message content with the correct keyboard sortcut for the current
+  // platform.
+  welcomeMessage.textContent = aboutDevtoolsBundle.formatStringFromName("welcome.message",
+    [inspectorShortcut], 1);
 
   // Set the appropriate title message.
   if (reason == "ContextMenu") {
     document.getElementById("inspect-title").removeAttribute("hidden");
   } else {
     document.getElementById("common-title").removeAttribute("hidden");
   }
 
@@ -164,16 +183,30 @@ window.addEventListener("load", function
 
   let featuresContainer = document.querySelector(".features-list");
   for (let feature of features) {
     featuresContainer.appendChild(createFeatureEl(feature));
   }
 
   // Update the current page based on the current value of DEVTOOLS_ENABLED_PREF.
   updatePage();
+
+  try {
+    if (reason) {
+      Services.telemetry.getHistogramById(TELEMETRY_OPENED_REASON).add(reason);
+    }
+
+    if (keyid) {
+      Services.telemetry.getHistogramById(TELEMETRY_OPENED_KEY).add(keyid);
+    }
+
+    Services.telemetry.scalarAdd(TELEMETRY_OPENED, 1);
+  } catch (e) {
+    dump("about:devtools onload telemetry failed: " + e + "\n");
+  }
 }, { once: true });
 
 window.addEventListener("beforeunload", function () {
   // Focus the tab that triggered the DevTools onboarding.
   if (document.visibilityState != "visible") {
     // Only try to focus the correct tab if the current tab is the about:devtools page.
     return;
   }
@@ -189,9 +222,18 @@ window.addEventListener("beforeunload", 
     gBrowser.selectedTab = originalTab;
   }
 }, {once: true});
 
 window.addEventListener("unload", function () {
   document.getElementById("install").removeEventListener("click", onInstallButtonClick);
   document.getElementById("close").removeEventListener("click", onCloseButtonClick);
   Services.prefs.removeObserver(DEVTOOLS_ENABLED_PREF, updatePage);
+
+  const isEnabled = Services.prefs.getBoolPref("devtools.enabled");
+  if (!isEnabledOnLoad && !isEnabled) {
+    try {
+      Services.telemetry.scalarAdd(TELEMETRY_NOINSTALL_EXITS, 1);
+    } catch (e) {
+      dump("about:devtools onunload telemetry failed: " + e + "\n");
+    }
+  }
 }, {once: true});

--- a/devtools/shim/aboutdevtools/aboutdevtools.xhtml
+++ b/devtools/shim/aboutdevtools/aboutdevtools.xhtml
@@ -1,16 +1,16 @@
 <?xml version="1.0" encoding="utf-8"?>
 <!-- This Source Code Form is subject to the terms of the Mozilla Public
    - License, v. 2.0. If a copy of the MPL was not distributed with this
    - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
 <!DOCTYPE html [
 <!ENTITY % htmlDTD PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "DTD/xhtml1-strict.dtd"> %htmlDTD;
 <!ENTITY % globalDTD SYSTEM "chrome://global/locale/global.dtd"> %globalDTD;
-<!ENTITY % aboutdevtoolsDTD SYSTEM "chrome://devtools-shim/content/aboutdevtools/tmp-locale/aboutdevtools.dtd"> %aboutdevtoolsDTD;
+<!ENTITY % aboutdevtoolsDTD SYSTEM "chrome://devtools-shim/locale/aboutdevtools.dtd"> %aboutdevtoolsDTD;
 ]>
 
 <html xmlns="http://www.w3.org/1999/xhtml" dir="&locale.dir;">
 <head>
   <title>&aboutDevtools.headTitle;</title>
   <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>a
   <link rel="stylesheet" href="chrome://global/skin/in-content/common.css" type="text/css"/>
   <link rel="stylesheet" href="chrome://devtools-shim/content/aboutdevtools/aboutdevtools.css"  type="text/css"/>
@@ -31,30 +31,32 @@
         <p id="about-debugging-message" hidden="true">&aboutDevtools.enable.aboutDebuggingMessage;</p>
         <p id="menu-message" hidden="true">&aboutDevtools.enable.menuMessage;</p>
         <p id="key-shortcut-message" hidden="true">&aboutDevtools.enable.keyShortcutMessage;</p>
         <p id="inspect-element-message" hidden="true">&aboutDevtools.enable.inspectElementMessage;</p>
 
         <p>&aboutDevtools.enable.commonMessage;</p>
         <a class="external installpage-link" href="https://developer.mozilla.org/docs/Tools" target="_blank">&aboutDevtools.enable.learnMoreLink;</a>
         <div class="buttons-container">
-          <button class="primary-button" id="install">&aboutDevtools.enable.installButton;</button>
+          <button class="primary-button" id="install">&aboutDevtools.enable.enableButton;</button>
           <button class="default-button" id="close">&aboutDevtools.enable.closeButton;</button>
         </div>
       </div>
     </div>
   </div>
 
   <!-- This page, hidden by default is displayed once the add-on is installed -->
   <div id="welcome-page" class="wrapper" hidden="true">
     <div class="box">
       <div class="left-pane" />
       <div class="right-pane">
         <h1 class="title" >&aboutDevtools.welcome.title;</h1>
-        <p id="welcome-message">&aboutDevtools.welcome.message;</p>
+        <!-- The welcome message is dynamically updated with a keyboard shortcut at
+             runtime and added in aboutdevtools.js -->
+        <p id="welcome-message"></p>
 
         <!-- Form dedicated to the newsletter subscription -->
         <div class="newsletter">
           <h2 class="newsletter-title">&aboutDevtools.newsletter.title;</h2>
           <p>&aboutDevtools.newsletter.message;</p>
 
           <form id="newsletter-form" name="newsletter-form" action="https://www.mozilla.org/en-US/newsletter/" method="post">
             <!-- "H" stands for the HTML format (->fmt). Alternative is T for text. -->
@@ -65,17 +67,17 @@
             <section id="newsletter-email" class="newsletter-form-section">
               <input type="email" id="email" name="email" required="true" placeholder="&aboutDevtools.newsletter.email.placeholder;" />
             </section>
 
             <section id="newsletter-privacy" class="newsletter-form-section">
               <input type="checkbox" id="privacy" name="privacy" required="true" />
               <label for="privacy">&aboutDevtools.newsletter.privacy.label;</label>
             </section>
-            <button type="submit" id="newsletter-submit" class="primary-button">&aboutDevtools.newsletter.subscribe.label;</button>
+            <button type="submit" id="newsletter-submit" class="primary-button">&aboutDevtools.newsletter.subscribeButton;</button>
           </form>
           <div id="newsletter-thanks">
             <h2>&aboutDevtools.newsletter.thanks.title;</h2>
             <p>&aboutDevtools.newsletter.thanks.message;</p>
           </div>
         </div>
       </div>
     </div>
@@ -85,20 +87,19 @@
       </ul>
     </div>
 
     <footer>
       <img class="dev-edition-logo"
            src="chrome://devtools-shim/content/aboutdevtools/images/dev-edition-logo.svg"
            alt="Firefox Developer Edition logo"/>
       <div class="footer-message">
-        <h1 class="footer-message-title">Firefox Developer Edition</h1>
-        <p>
-          Looking for more than just Developer Tools?
-          Check out the Firefox browser that is built specifically for developers and modern workflows.
-        </p>
-        <a class="external footer-link" href="https://www.mozilla.org/en-US/firefox/developer/" target="_blank">Learn more</a>
+        <h1 class="footer-message-title">&aboutDevtools.footer.title;</h1>
+        <p>&aboutDevtools.footer.message;</p>
+        <a class="external footer-link"
+           href="https://www.mozilla.org/firefox/developer/"
+           target="_blank">&aboutDevtools.footer.learnMoreLink;</a>
       </div>
     </footer>
   </div>
 
 </body>
 </html>

--- a/devtools/shim/devtools-startup.js
+++ b/devtools/shim/devtools-startup.js
@@ -460,24 +460,25 @@ DevToolsStartup.prototype = {
     // Appending a <key> element is not always enough. The <keyset> needs
     // to be detached and reattached to make sure the <key> is taken into
     // account (see bug 832984).
     let mainKeyset = doc.getElementById("mainKeyset");
     mainKeyset.parentNode.insertBefore(keyset, mainKeyset);
   },
 
   onKey(window, key) {
-    // Record the timing at which this event started in order to compute later in
-    // gDevTools.showToolbox, the complete time it takes to open the toolbox.
-    // i.e. especially take `initDevTools` into account.
-
-    let startTime = window.performance.now();
-    let require = this.initDevTools("KeyShortcut");
-    if (require) {
-      // require might be null if initDevTools was called while DevTools are disabled.
+    if (!Services.prefs.getBoolPref(DEVTOOLS_ENABLED_PREF)) {
+      let id = key.toolId || key.id;
+      this.openInstallPage("KeyShortcut", id);
+    } else {
+      // Record the timing at which this event started in order to compute later in
+      // gDevTools.showToolbox, the complete time it takes to open the toolbox.
+      // i.e. especially take `initDevTools` into account.
+      let startTime = window.performance.now();
+      let require = this.initDevTools("KeyShortcut");
       let { gDevToolsBrowser } = require("devtools/client/framework/devtools-browser");
       gDevToolsBrowser.onKeyShortcut(window, key, startTime);
     }
   },
 
   // Create a <xul:key> DOM Element
   createKey(doc, { id, toolId, shortcut, modifiers: mod }, oncommand) {
     let k = doc.createElement("key");
@@ -523,17 +524,27 @@ DevToolsStartup.prototype = {
     this.initialized = true;
     let { require } = Cu.import("resource://devtools/shared/Loader.jsm", {});
     // Ensure loading main devtools module that hooks up into browser UI
     // and initialize all devtools machinery.
     require("devtools/client/framework/devtools-browser");
     return require;
   },
 
-  openInstallPage: function (reason) {
+  /**
+   * Open about:devtools to start the onboarding flow.
+   *
+   * @param {String} reason
+   *        One of "KeyShortcut", "SystemMenu", "HamburgerMenu", "ContextMenu",
+   *        "CommandLine".
+   * @param {String} keyId
+   *        Optional. If the onboarding flow was triggered by a keyboard shortcut, pass
+   *        the shortcut key id (or toolId) to about:devtools.
+   */
+  openInstallPage: function (reason, keyId) {
     let { gBrowser } = Services.wm.getMostRecentWindow("navigator:browser");
 
     // Focus about:devtools tab if there is already one opened in the current window.
     for (let tab of gBrowser.tabs) {
       let browser = tab.linkedBrowser;
       // browser.documentURI might be undefined if the browser tab is still loading.
       let location = browser.documentURI ? browser.documentURI.spec : "";
       if (location.startsWith("about:devtools") &&
@@ -551,16 +562,20 @@ DevToolsStartup.prototype = {
       params.push("reason=" + encodeURIComponent(reason));
     }
 
     let selectedBrowser = gBrowser.selectedBrowser;
     if (selectedBrowser) {
       params.push("tabid=" + selectedBrowser.outerWindowID);
     }
 
+    if (keyId) {
+      params.push("keyid=" + keyId);
+    }
+
     if (params.length > 0) {
       url += "?" + params.join("&");
     }
 
     // Set relatedToCurrent: true to open the tab next to the current one.
     gBrowser.selectedTab = gBrowser.addTab(url, {relatedToCurrent: true});
   },
 

--- a/devtools/shim/jar.mn
+++ b/devtools/shim/jar.mn
@@ -7,20 +7,16 @@ devtools-shim.jar:
     content/aboutdevtools/aboutdevtools.xhtml  (aboutdevtools/aboutdevtools.xhtml)
     content/aboutdevtools/aboutdevtools.css (aboutdevtools/aboutdevtools.css)
     content/aboutdevtools/aboutdevtools.js (aboutdevtools/aboutdevtools.js)
     content/aboutdevtools/subscribe.css (aboutdevtools/subscribe.css)
     content/aboutdevtools/subscribe.js (aboutdevtools/subscribe.js)
 
     content/aboutdevtools/images/otter.svg (aboutdevtools/images/otter.svg)
 
-    # Temporary localisation file, move back to devtools/shim/locales/en-US when ready for localization
-    # See https://bugzilla.mozilla.org/show_bug.cgi?id=1408369
-    content/aboutdevtools/tmp-locale/aboutdevtools.dtd (aboutdevtools/tmp-locale/aboutdevtools.dtd)
-
     content/aboutdevtools/images/dev-edition-logo.svg (aboutdevtools/images/dev-edition-logo.svg)
     content/aboutdevtools/images/external-link.svg (aboutdevtools/images/external-link.svg)
     content/aboutdevtools/images/feature-inspector.svg (aboutdevtools/images/feature-inspector.svg)
     content/aboutdevtools/images/feature-console.svg (aboutdevtools/images/feature-console.svg)
     content/aboutdevtools/images/feature-debugger.svg (aboutdevtools/images/feature-debugger.svg)
     content/aboutdevtools/images/feature-network.svg (aboutdevtools/images/feature-network.svg)
     content/aboutdevtools/images/feature-memory.svg (aboutdevtools/images/feature-memory.svg)
     content/aboutdevtools/images/feature-visualediting.svg (aboutdevtools/images/feature-visualediting.svg)

rename from devtools/shim/aboutdevtools/tmp-locale/aboutdevtools.dtd
rename to devtools/shim/locales/en-US/aboutdevtools.dtd
--- a/devtools/shim/aboutdevtools/tmp-locale/aboutdevtools.dtd
+++ b/devtools/shim/locales/en-US/aboutdevtools.dtd
@@ -1,35 +1,78 @@
 <!-- This Source Code Form is subject to the terms of the Mozilla Public
    - License, v. 2.0. If a copy of the MPL was not distributed with this
    - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
 
+<!-- LOCALIZATION NOTE : This file contains the strings used in aboutdevtools.xhtml,
+  -  displayed when going to about:devtools. UI depends on the value of the preference
+  -  "devtools.enabled".
+  -
+  -  "aboutDevtools.enable.*" and "aboutDevtools.newsletter.*" keys are used when DevTools
+     are disabled
+  -  "aboutDevtools.welcome.*" keys are used when DevTools are enabled
+  - -->
+
+<!-- LOCALIZATION NOTE (aboutDevtools.headTitle): Text of the title tag for about:devtools -->
 <!ENTITY  aboutDevtools.headTitle "About Developer Tools">
+
+<!-- LOCALIZATION NOTE (aboutDevtools.enable.title): Title of the top about:devtools
+  -  section displayed when DevTools are disabled. -->
 <!ENTITY  aboutDevtools.enable.title "Enable Firefox Developer Tools">
+
+<!-- LOCALIZATION NOTE (aboutDevtools.enable.inspectElementTitle): Title of the top
+  -  section displayed when devtools are disabled and the user triggered DevTools by using
+  -  the Inspect Element menu item. -->
 <!ENTITY  aboutDevtools.enable.inspectElementTitle "Enable Firefox Developer Tools to use Inspect Element">
 
+<!-- LOCALIZATION NOTE (aboutDevtools.enable.inspectElementMessage): Message displayed
+  -  when users come from using the Inspect Element menu item. -->
+<!ENTITY  aboutDevtools.enable.inspectElementMessage
+          "Examine and edit HTML and CSS with the Developer Tools’ Inspector.">
+
+<!-- LOCALIZATION NOTE (aboutDevtools.enable.aboutDebuggingMessage): Message displayed
+  -  when users come from about:debugging. -->
 <!ENTITY  aboutDevtools.enable.aboutDebuggingMessage
-          "Develop and debug WebExtensions, web workers, service workers and more with Firefox DevTools.">
-<!ENTITY  aboutDevtools.enable.inspectElementMessage
-          "Examine and edit HTML and CSS with the DevTools Inspector.">
+          "Develop and debug WebExtensions, web workers, service workers and more with Firefox Developer Tools.">
+
+<!-- LOCALIZATION NOTE (aboutDevtools.enable.keyShortcutMessage): Message displayed when
+  -  users pressed a DevTools key shortcut. -->
 <!ENTITY  aboutDevtools.enable.keyShortcutMessage
           "You activated a Developer Tools shortcut. If that was a mistake, you can close this tab.">
+
+<!-- LOCALIZATION NOTE (aboutDevtools.enable.menuMessage): Message displayed when users
+  -  clicked on a "Enable Developer Tools" menu item. -->
 <!ENTITY  aboutDevtools.enable.menuMessage
           "Examine, edit and debug HTML, CSS, and JavaScript with tools like Inspector and Debugger.">
 
+<!-- LOCALIZATION NOTE (aboutDevtools.enable.commonMessage): Generic message displayed for
+  -  all possible entry points (keyshortcut, menu item etc…). -->
 <!ENTITY  aboutDevtools.enable.commonMessage
-          "As of Firefox 58, Developer Tools are disabled by default to give you more control over your browser.">
+          "Firefox Developer Tools are disabled by default to give you more control over your browser.">
 
-<!ENTITY  aboutDevtools.enable.learnMoreLink "Learn more about DevTools">
-<!ENTITY  aboutDevtools.enable.installButton "Enable Developer Tools">
+<!-- LOCALIZATION NOTE (aboutDevtools.enable.learnMoreLink): Text for the link to
+  -  https://developer.mozilla.org/docs/Tools displayed in the top section when DevTools
+  -  are disabled. -->
+<!ENTITY  aboutDevtools.enable.learnMoreLink "Learn more about Developer Tools">
+
+<!ENTITY  aboutDevtools.enable.enableButton "Enable Developer Tools">
 <!ENTITY  aboutDevtools.enable.closeButton "Close this page">
+
 <!ENTITY  aboutDevtools.welcome.title "Welcome to Firefox Developer Tools!">
-<!ENTITY  aboutDevtools.welcome.message "You’ve successfully enabled DevTools! To get started, explore the Web Developer menu or open the tools with ##INSPECTOR_SHORTCUT##.">
 
 <!ENTITY  aboutDevtools.newsletter.title "Mozilla Developer Newsletter">
+<!-- LOCALIZATION NOTE (aboutDevtools.newsletter.message): Subscribe form message.
+  -  The newsletter is only available in english at the moment.
+  -  See Bug 1415273 for support of additional languages.-->
 <!ENTITY  aboutDevtools.newsletter.message "Get developer news, tricks and resources sent straight to your inbox.">
 <!ENTITY  aboutDevtools.newsletter.email.placeholder "Email">
-<!ENTITY  aboutDevtools.newsletter.privacy.label "I’m okay with Mozilla handling my info as explained in this <a class=&#x0022;external&#x0022; href=&#x0022;https://www.mozilla.org/privacy/&#x0022;>Privacy Policy</a>.">
-<!ENTITY  aboutDevtools.newsletter.subscribe.label "Subscribe">
-
+<!ENTITY  aboutDevtools.newsletter.privacy.label "I’m okay with Mozilla handling my info as explained in this <a class='external' href='https://www.mozilla.org/privacy/'>Privacy Policy</a>.">
+<!ENTITY  aboutDevtools.newsletter.subscribeButton "Subscribe">
 <!ENTITY  aboutDevtools.newsletter.thanks.title "Thanks!">
 <!ENTITY  aboutDevtools.newsletter.thanks.message "If you haven’t previously confirmed a subscription to a Mozilla-related newsletter you may have to do so. Please check your inbox or your spam filter for an email from us.">
 
+<!ENTITY  aboutDevtools.footer.title "Firefox Developer Edition">
+<!ENTITY  aboutDevtools.footer.message "Looking for more than just Developer Tools? Check out the Firefox browser that is built specifically for developers and modern workflows.">
+
+<!-- LOCALIZATION NOTE (aboutDevtools.footer.learnMoreLink): Text for the link to
+  -  https://www.mozilla.org/firefox/developer/ displayed in the footer. -->
+<!ENTITY  aboutDevtools.footer.learnMoreLink "Learn more">
+

--- a/devtools/shim/locales/en-US/aboutdevtools.properties
+++ b/devtools/shim/locales/en-US/aboutdevtools.properties
@@ -43,8 +43,12 @@ newsletter.error.common=Subscription req
 
 # LOCALIZATION NOTE (newsletter.error.unknown): error text displayed when the newsletter
 # subscription failed for an unexpected reason.
 newsletter.error.unknown=An unexpected error occurred.
 
 # LOCALIZATION NOTE (newsletter.error.timeout): error text displayed when the newsletter
 # subscription timed out.
 newsletter.error.timeout=Subscription request timed out.
+
+# LOCALIZATION NOTE (welcome.message): Message displayed when devtools are enabled.
+# %S will be replaced with the shortcut to toggle the DevTools toolbox.
+welcome.message=You’ve successfully enabled Developer Tools! To get started, explore the Web Developer menu or open the tools with %S.

--- a/dom/base/Element.cpp
+++ b/dom/base/Element.cpp
@@ -1209,17 +1209,17 @@ Element::CreateShadowRoot(ErrorResult& a
 
 already_AddRefed<ShadowRoot>
 Element::AttachShadowInternal(bool aClosed, ErrorResult& aError)
 {
   /**
    * 3. If context object is a shadow host, then throw
    *    an "InvalidStateError" DOMException.
    */
-  if (GetShadowRoot()) {
+  if (GetShadowRoot() || GetXBLBinding()) {
     aError.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
     return nullptr;
   }
 
   nsAutoScriptBlocker scriptBlocker;
 
   RefPtr<mozilla::dom::NodeInfo> nodeInfo;
   nodeInfo = mNodeInfo->NodeInfoManager()->GetNodeInfo(

--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -1593,17 +1593,18 @@ nsIDocument::nsIDocument()
     mInSyncOperationCount(0),
     mBlockDOMContentLoaded(0),
     mUseCounters(0),
     mChildDocumentUseCounters(0),
     mNotifiedPageForUseCounter(0),
     mIncCounters(),
     mUserHasInteracted(false),
     mServoRestyleRootDirtyBits(0),
-    mThrowOnDynamicMarkupInsertionCounter(0)
+    mThrowOnDynamicMarkupInsertionCounter(0),
+    mIgnoreOpensDuringUnloadCounter(0)
 {
   SetIsInDocument();
   for (auto& cnt : mIncCounters) {
     cnt = 0;
   }
 }
 
 nsDocument::nsDocument(const char* aContentType)

--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -3221,16 +3221,32 @@ public:
   }
 
   void DecrementThrowOnDynamicMarkupInsertionCounter()
   {
     MOZ_ASSERT(mThrowOnDynamicMarkupInsertionCounter);
     --mThrowOnDynamicMarkupInsertionCounter;
   }
 
+  bool ShouldIgnoreOpens() const
+  {
+    return mIgnoreOpensDuringUnloadCounter;
+  }
+
+  void IncrementIgnoreOpensDuringUnloadCounter()
+  {
+    ++mIgnoreOpensDuringUnloadCounter;
+  }
+
+  void DecrementIgnoreOpensDuringUnloadCounter()
+  {
+    MOZ_ASSERT(mIgnoreOpensDuringUnloadCounter);
+    --mIgnoreOpensDuringUnloadCounter;
+  }
+
   virtual bool AllowPaymentRequest() const = 0;
   virtual void SetAllowPaymentRequest(bool aAllowPaymentRequest) = 0;
 
 protected:
   bool GetUseCounter(mozilla::UseCounter aUseCounter)
   {
     return mUseCounters[aUseCounter];
   }
@@ -3778,16 +3794,19 @@ protected:
   // root corresponds to.
   nsCOMPtr<nsINode> mServoRestyleRoot;
   uint32_t mServoRestyleRootDirtyBits;
 
   // Used in conjunction with the create-an-element-for-the-token algorithm to
   // prevent custom element constructors from being able to use document.open(),
   // document.close(), and document.write() when they are invoked by the parser.
   uint32_t mThrowOnDynamicMarkupInsertionCounter;
+
+  // Count of unload/beforeunload/pagehide operations in progress.
+  uint32_t mIgnoreOpensDuringUnloadCounter;
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(nsIDocument, NS_IDOCUMENT_IID)
 
 /**
  * mozAutoSubtreeModified batches DOM mutations so that a DOMSubtreeModified
  * event is dispatched, if necessary, when the outermost mozAutoSubtreeModified
  * object is deleted.
@@ -3851,16 +3870,33 @@ class MOZ_RAII AutoSetThrowOnDynamicMark
     ~AutoSetThrowOnDynamicMarkupInsertionCounter() {
       mDocument->DecrementThrowOnDynamicMarkupInsertionCounter();
     }
 
   private:
     nsIDocument* mDocument;
 };
 
+class MOZ_RAII IgnoreOpensDuringUnload final
+{
+public:
+  explicit IgnoreOpensDuringUnload(nsIDocument* aDoc)
+    : mDoc(aDoc)
+  {
+    mDoc->IncrementIgnoreOpensDuringUnloadCounter();
+  }
+
+  ~IgnoreOpensDuringUnload()
+  {
+    mDoc->DecrementIgnoreOpensDuringUnloadCounter();
+  }
+private:
+  nsIDocument* mDoc;
+};
+
 // XXX These belong somewhere else
 nsresult
 NS_NewHTMLDocument(nsIDocument** aInstancePtrResult, bool aLoadedAsData = false);
 
 nsresult
 NS_NewXMLDocument(nsIDocument** aInstancePtrResult, bool aLoadedAsData = false,
                   bool aIsPlainDocument = false);
 

new file mode 100644
--- /dev/null
+++ b/dom/html/crashtests/1412173.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<head>
+<script>
+let f = document.createElement('frame');
+f.onload = function() {
+  let frameDocument = f.contentDocument;
+  frameDocument.body.onbeforeunload = function () { frameDocument.write('<p>beforeUnload</p>') };
+  frameDocument.write('<p>trigger unload</p>')
+  window.stop();
+  document.documentElement.className = '';
+};
+document.documentElement.appendChild(f);
+</script>
+</head>
+<body>
+</body>
+</html>

--- a/dom/html/crashtests/crashtests.list
+++ b/dom/html/crashtests/crashtests.list
@@ -80,9 +80,10 @@ load 1237633.html
 load 1281972-1.html
 load 1282894.html
 load 1290904.html
 load 1343886-1.html
 load 1343886-2.xml
 load 1343886-3.xml
 load 1350972.html
 load 1386905.html
-asserts(0-4) load 1401726.html
\ No newline at end of file
+asserts(0-4) load 1401726.html
+load 1412173.html

--- a/dom/html/nsHTMLDocument.cpp
+++ b/dom/html/nsHTMLDocument.cpp
@@ -1529,16 +1529,23 @@ nsHTMLDocument::Open(JSContext* cx,
     // invoked."
     // Note that aborting a parser leaves the parser "active" with its
     // insertion point "not undefined". We track this using mParserAborted,
     // because aborting a parser nulls out mParser.
     nsCOMPtr<nsIDocument> ret = this;
     return ret.forget();
   }
 
+  // Implement Step 6 of:
+  // https://html.spec.whatwg.org/multipage/dynamic-markup-insertion.html#document-open-steps
+  if (ShouldIgnoreOpens()) {
+    nsCOMPtr<nsIDocument> ret = this;
+    return ret.forget();
+  }
+
   // No calling document.open() without a script global object
   if (!mScriptGlobalObject) {
     nsCOMPtr<nsIDocument> ret = this;
     return ret.forget();
   }
 
   nsPIDOMWindowOuter* outer = GetWindow();
   if (!outer || (GetInnerWindow() != outer->GetCurrentInnerWindow())) {
@@ -1942,16 +1949,22 @@ nsHTMLDocument::WriteCommon(JSContext *c
 
   if (mParserAborted) {
     // Hixie says aborting the parser doesn't undefine the insertion point.
     // However, since we null out mParser in that case, we track the
     // theoretically defined insertion point using mParserAborted.
     return NS_OK;
   }
 
+  // Implement Step 4.1 of:
+  // https://html.spec.whatwg.org/multipage/dynamic-markup-insertion.html#document-write-steps
+  if (ShouldIgnoreOpens()) {
+    return NS_OK;
+  }
+
   nsresult rv = NS_OK;
 
   void *key = GenerateParserKey();
   if (mParser && !mParser->IsInsertionPointDefined()) {
     if (mIgnoreDestructiveWritesCounter) {
       // Instead of implying a call to document.open(), ignore the call.
       nsContentUtils::ReportToConsole(nsIScriptError::warningFlag,
                                       NS_LITERAL_CSTRING("DOM Events"), this,

--- a/extensions/cookie/test/browser.ini
+++ b/extensions/cookie/test/browser.ini
@@ -1,10 +1,13 @@
 [DEFAULT]
 
 [browser_test_favicon.js]
+support-files =
+  damonbowling.jpg
+  damonbowling.jpg^headers^
 [browser_permmgr_sync.js]
 # The browser_permmgr_sync test tests e10s specific behavior, and runs code
 # paths which would hit the debug only assertion in
 # nsPermissionManager::PermissionKey::CreateFromPrincipal. Because of this, it
 # is only run in e10s opt builds.
 skip-if = debug || !e10s
 [browser_permmgr_viewsrc.js]

--- a/extensions/cookie/test/browser_test_favicon.js
+++ b/extensions/cookie/test/browser_test_favicon.js
@@ -1,28 +1,23 @@
 // tests third party cookie blocking using a favicon load directly from chrome.
 // in this case, the docshell of the channel is chrome, not content; thus
 // the cookie should be considered third party.
 
-function test() {
-  waitForExplicitFinish();
-
-  Services.prefs.setIntPref("network.cookie.cookieBehavior", 1);
+add_task(async function() {
+  const iconUrl = "http://example.org/browser/extensions/cookie/test/damonbowling.jpg";
+	await SpecialPowers.pushPrefEnv({"set": [["network.cookie.cookieBehavior", 1]]});
 
-  Services.obs.addObserver(function (theSubject, theTopic, theData) {
-    var uri = theSubject.QueryInterface(Components.interfaces.nsIURI);
-    var domain = uri.host;
-
-    if (domain == "example.org") {
-      ok(true, "foreign favicon cookie was blocked");
+  let promise = TestUtils.topicObserved("cookie-rejected", subject => {
+    let uri = subject.QueryInterface(Components.interfaces.nsIURI);
+    return uri.spec == iconUrl;
+  });
 
-      Services.prefs.setIntPref("network.cookie.cookieBehavior", 0);
-
-      Services.obs.removeObserver(arguments.callee, "cookie-rejected");
+  let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, "http://example.com/");
+  registerCleanupFunction(async function() {
+    await BrowserTestUtils.removeTab(tab);
+  });
 
-      finish();
-    }
-  }, "cookie-rejected");
-
-  // kick off a favicon load
-  gBrowser.setIcon(gBrowser.selectedTab, "http://example.org/tests/extensions/cookie/test/damonbowling.jpg",
-                   Services.scriptSecurityManager.getSystemPrincipal());
-}
+  // Kick off a favicon load.
+  gBrowser.setIcon(tab, iconUrl);
+  await promise;
+  ok(true, "foreign favicon cookie was blocked");
+});

--- a/extensions/cookie/test/mochitest.ini
+++ b/extensions/cookie/test/mochitest.ini
@@ -1,14 +1,12 @@
 [DEFAULT]
 support-files =
   beltzner.jpg
   beltzner.jpg^headers^
-  damonbowling.jpg
-  damonbowling.jpg^headers^
   file_chromecommon.js
   file_domain_hierarchy_inner.html
   file_domain_hierarchy_inner_inner.html
   file_domain_hierarchy_inner_inner_inner.html
   file_domain_inner.html
   file_domain_inner_inner.html
   file_image_inner.html
   file_image_inner_inner.html

--- a/gfx/src/nsFont.cpp
+++ b/gfx/src/nsFont.cpp
@@ -37,42 +37,52 @@ nsFont::nsFont()
 }
 
 nsFont::~nsFont()
 {
 }
 
 bool nsFont::Equals(const nsFont& aOther) const
 {
-  if ((style == aOther.style) &&
-      (systemFont == aOther.systemFont) &&
-      (weight == aOther.weight) &&
-      (stretch == aOther.stretch) &&
-      (size == aOther.size) &&
-      (sizeAdjust == aOther.sizeAdjust) &&
-      (fontlist == aOther.fontlist) &&
-      (kerning == aOther.kerning) &&
-      (synthesis == aOther.synthesis) &&
-      (fontFeatureSettings == aOther.fontFeatureSettings) &&
-      (fontVariationSettings == aOther.fontVariationSettings) &&
-      (languageOverride == aOther.languageOverride) &&
-      (variantAlternates == aOther.variantAlternates) &&
-      (variantCaps == aOther.variantCaps) &&
-      (variantEastAsian == aOther.variantEastAsian) &&
-      (variantLigatures == aOther.variantLigatures) &&
-      (variantNumeric == aOther.variantNumeric) &&
-      (variantPosition == aOther.variantPosition) &&
-      (variantWidth == aOther.variantWidth) &&
-      (alternateValues == aOther.alternateValues) &&
-      (featureValueLookup == aOther.featureValueLookup) &&
-      (smoothing == aOther.smoothing) &&
-      (fontSmoothingBackgroundColor == aOther.fontSmoothingBackgroundColor)) {
-    return true;
+  return CalcDifference(aOther) == MaxDifference::eNone;
+}
+
+nsFont::MaxDifference
+nsFont::CalcDifference(const nsFont& aOther) const
+{
+  if ((style != aOther.style) ||
+      (systemFont != aOther.systemFont) ||
+      (weight != aOther.weight) ||
+      (stretch != aOther.stretch) ||
+      (size != aOther.size) ||
+      (sizeAdjust != aOther.sizeAdjust) ||
+      (fontlist != aOther.fontlist) ||
+      (kerning != aOther.kerning) ||
+      (synthesis != aOther.synthesis) ||
+      (fontFeatureSettings != aOther.fontFeatureSettings) ||
+      (fontVariationSettings != aOther.fontVariationSettings) ||
+      (languageOverride != aOther.languageOverride) ||
+      (variantAlternates != aOther.variantAlternates) ||
+      (variantCaps != aOther.variantCaps) ||
+      (variantEastAsian != aOther.variantEastAsian) ||
+      (variantLigatures != aOther.variantLigatures) ||
+      (variantNumeric != aOther.variantNumeric) ||
+      (variantPosition != aOther.variantPosition) ||
+      (variantWidth != aOther.variantWidth) ||
+      (alternateValues != aOther.alternateValues) ||
+      (featureValueLookup != aOther.featureValueLookup)) {
+    return MaxDifference::eLayoutAffecting;
   }
-  return false;
+
+  if ((smoothing != aOther.smoothing) ||
+      (fontSmoothingBackgroundColor != aOther.fontSmoothingBackgroundColor)) {
+    return MaxDifference::eVisual;
+  }
+
+  return MaxDifference::eNone;
 }
 
 nsFont& nsFont::operator=(const nsFont& aOther) = default;
 
 void
 nsFont::CopyAlternates(const nsFont& aOther)
 {
   variantAlternates = aOther.variantAlternates;

--- a/gfx/src/nsFont.h
+++ b/gfx/src/nsFont.h
@@ -138,16 +138,24 @@ struct nsFont {
   bool operator!=(const nsFont& aOther) const {
     return !Equals(aOther);
   }
 
   bool Equals(const nsFont& aOther) const;
 
   nsFont& operator=(const nsFont& aOther);
 
+  enum class MaxDifference : uint8_t {
+    eNone,
+    eVisual,
+    eLayoutAffecting
+  };
+
+  MaxDifference CalcDifference(const nsFont& aOther) const;
+
   void CopyAlternates(const nsFont& aOther);
 
   // Add featureSettings into style
   void AddFontFeaturesToStyle(gfxFontStyle *aStyle,
                               bool aVertical) const;
 
   void AddFontVariationsToStyle(gfxFontStyle *aStyle) const;
 };

--- a/gfx/tests/gtest/TestRect.cpp
+++ b/gfx/tests/gtest/TestRect.cpp
@@ -4,16 +4,17 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #include <limits>
 
 #include "gtest/gtest.h"
 
 #include "nsRect.h"
 #include "gfxRect.h"
+#include "mozilla/WritingModes.h"
 #ifdef XP_WIN
 #include <windows.h>
 #endif
 
 template <class RectType>
 static bool
 TestConstructors()
 {
@@ -440,17 +441,65 @@ TestSwap()
 {
   RectType  rect(1, 2, 3, 4);
   EXPECT_TRUE(rect.X() == 1 && rect.Y() == 2 && rect.Width() == 3 && rect.Height() == 4);
   rect.Swap();
   EXPECT_TRUE(rect.X() == 2 && rect.Y() == 1 && rect.Width() == 4 && rect.Height() == 3);
   return true;
 }
 
+static void
+TestIntersectionLogicalHelper(nscoord x1, nscoord y1, nscoord w1, nscoord h1,
+                              nscoord x2, nscoord y2, nscoord w2, nscoord h2,
+                              nscoord xR, nscoord yR, nscoord wR, nscoord hR,
+                              bool isNonEmpty)
+{
+  nsRect rect1(x1, y1, w1, h1);
+  nsRect rect2(x2, y2, w2, h2);
+  nsRect rectDebug;
+  EXPECT_TRUE(isNonEmpty == rectDebug.IntersectRect(rect1, rect2));
+  EXPECT_TRUE(rectDebug.IsEqualEdges(nsRect(xR, yR, wR, hR)));
 
+  mozilla::LogicalRect r1(mozilla::WritingMode(), rect1.X(), rect1.Y(), rect1.Width(), rect1.Height());
+  mozilla::LogicalRect r2(mozilla::WritingMode(), rect2.X(), rect2.Y(), rect2.Width(), rect2.Height());
+  EXPECT_TRUE(isNonEmpty == r1.IntersectRect(r1, r2));
+  EXPECT_TRUE(rectDebug.IsEqualEdges(nsRect(r1.IStart(WritingMode()), r1.BStart(WritingMode()),
+                                            r1.ISize(WritingMode()), r1.BSize(WritingMode()))));
+
+  mozilla::LogicalRect r3(mozilla::WritingMode(), rect1.X(), rect1.Y(), rect1.Width(), rect1.Height());
+  mozilla::LogicalRect r4(mozilla::WritingMode(), rect2.X(), rect2.Y(), rect2.Width(), rect2.Height());
+  EXPECT_TRUE(isNonEmpty == r4.IntersectRect(r3, r4));
+  EXPECT_TRUE(rectDebug.IsEqualEdges(nsRect(r4.IStart(WritingMode()), r4.BStart(WritingMode()),
+                                            r4.ISize(WritingMode()), r4.BSize(WritingMode()))));
+
+  mozilla::LogicalRect r5(mozilla::WritingMode(), rect1.X(), rect1.Y(), rect1.Width(), rect1.Height());
+  mozilla::LogicalRect r6(mozilla::WritingMode(), rect2.X(), rect2.Y(), rect2.Width(), rect2.Height());
+  mozilla::LogicalRect r7(mozilla::WritingMode(), 0, 0, 1, 1);
+  EXPECT_TRUE(isNonEmpty == r7.IntersectRect(r5, r6));
+  EXPECT_TRUE(rectDebug.IsEqualEdges(nsRect(r7.IStart(WritingMode()), r7.BStart(WritingMode()),
+                                            r7.ISize(WritingMode()), r7.BSize(WritingMode()))));
+}
+
+static void
+TestIntersectionLogical(nscoord x1, nscoord y1, nscoord w1, nscoord h1,
+                        nscoord x2, nscoord y2, nscoord w2, nscoord h2,
+                        nscoord xR, nscoord yR, nscoord wR, nscoord hR,
+                        bool isNonEmpty)
+{
+  TestIntersectionLogicalHelper(x1, y1, w1, h1, x2, y2, w2, h2, xR, yR, wR, hR, isNonEmpty);
+  TestIntersectionLogicalHelper(x2, y2, w2, h2, x1, y1, w1, h1, xR, yR, wR, hR, isNonEmpty);
+}
+
+TEST(Gfx, Logical)
+{
+  TestIntersectionLogical(578, 0, 2650, 1152, 1036, 0, 2312, 1, 1036, 0, 2192, 1, true);
+  TestIntersectionLogical(0, 0, 1000, 1000, 500, 500, 1000, 1000, 500, 500, 500, 500, true);
+  TestIntersectionLogical(100, 200, 300, 400, 50, 250, 100, 100, 100, 250, 50, 100, true);
+  TestIntersectionLogical(0, 100, 200, 300, 300, 100, 100, 300, 300, 100, 0, 0, false);
+}
 
 TEST(Gfx, nsRect) {
   TestConstructors<nsRect>();
   TestEqualityOperator<nsRect>();
   TestContainment<nsRect>();
   TestIntersects<nsRect>();
   TestIntersection<nsRect>();
   TestUnion<nsRect>();
@@ -478,8 +527,9 @@ TEST(Gfx, gfxRect) {
   TestIntersects<gfxRect>();
   TestIntersection<gfxRect>();
   TestUnion<gfxRect>();
   TestBug1135677<gfxRect>();
   TestFiniteGfx();
   TestSetWH<gfxRect>();
   TestSwap<gfxRect>();
 }
+

--- a/gfx/thebes/gfxFontFamilyList.h
+++ b/gfx/thebes/gfxFontFamilyList.h
@@ -441,11 +441,16 @@ protected:
     FontFamilyType             mDefaultFontType; // none, serif or sans-serif
 };
 
 inline bool
 operator==(const FontFamilyList& a, const FontFamilyList& b) {
     return a.Equals(b);
 }
 
+inline bool
+operator!=(const FontFamilyList& a, const FontFamilyList& b) {
+    return !a.Equals(b);
+}
+
 } // namespace mozilla
 
 #endif /* GFX_FONT_FAMILY_LIST_H */

--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -7473,40 +7473,21 @@ nsCSSFrameConstructor::GetRangeInsertion
   // real parent frame; if not, then the frame hasn't been built yet
   // and we just bail.
   InsertionPoint insertionPoint = GetInsertionPoint(aContainer, nullptr);
   if (!insertionPoint.mParentFrame && !insertionPoint.mMultiple) {
     return insertionPoint; // Don't build the frames.
   }
 
   if (insertionPoint.mMultiple || aStartChild->GetXBLInsertionPoint()) {
-    // We have an insertion point.  There are some additional tests we need to do
-    // in order to ensure that an append is a safe operation.
-    uint32_t childCount = 0;
-
-    if (!insertionPoint.mMultiple) {
-      // We may need to make multiple ContentInserted calls instead.  A
-      // reasonable heuristic to employ (in order to maintain good performance)
-      // is to find out if the insertion point's content node contains any
-      // explicit children.  If it does not, then it is highly likely that
-      // an append is occurring.  (Note it is not definite, and there are insane
-      // cases we will not deal with by employing this heuristic, but it beats
-      // always falling back to multiple ContentInserted calls).
-      //
-      // In the multiple insertion point case, we know we're going to need to do
-      // multiple ContentInserted calls anyway.
-      // XXXndeakin This test doesn't work in the new world. Or rather, it works, but
-      // it's slow
-      childCount = insertionPoint.mParentFrame->GetContent()->GetChildCount();
-    }
-
     // If we have multiple insertion points or if we have an insertion point
     // and the operation is not a true append or if the insertion point already
     // has explicit children, then we must fall back.
-    if (insertionPoint.mMultiple || aEndChild != nullptr || childCount > 0) {
+    if (insertionPoint.mMultiple || aEndChild ||
+        insertionPoint.mParentFrame->GetContent()->HasChildren()) {
       // Now comes the fun part.  For each inserted child, make a
       // ContentInserted call as if it had just gotten inserted and
       // let ContentInserted handle the mess.
       IssueSingleInsertNofications(aContainer, aStartChild, aEndChild,
                                    aInsertionKind);
       insertionPoint.mParentFrame = nullptr;
     }
   }
@@ -7850,29 +7831,24 @@ nsCSSFrameConstructor::ContentAppended(n
     // because processing a single caption can add a whole bunch of things to
     // the frame items due to pseudoframe processing.  So we'd have to pull
     // captions from a list anyway; might as well do that here.
     // XXXbz this is no longer true; we could pull captions directly out of the
     // FrameConstructionItemList now.
     PullOutCaptionFrames(frameItems, captionItems);
   }
 
-  bool dealtWithFirstLine = false;
   if (haveFirstLineStyle && parentFrame == containingBlock) {
     // It's possible that some of the new frames go into a
     // first-line frame. Look at them and see...
     AppendFirstLineFrames(state, containingBlock->GetContent(),
                           containingBlock, frameItems);
     // That moved things into line frames as needed, reparenting their
     // styles.  Nothing else needs to be done.
-    dealtWithFirstLine = true;
-  }
-
-  if (!dealtWithFirstLine &&
-      parentFrame->StyleContext()->HasPseudoElementData()) {
+  } else if (parentFrame->StyleContext()->HasPseudoElementData()) {
     // parentFrame might be inside a ::first-line frame.  Check whether it is,
     // and if so fix up our styles.
     CheckForFirstLineInsertion(parentFrame, frameItems);
     CheckForFirstLineInsertion(parentFrame, captionItems);
   }
 
   // Notify the parent frame passing it the list of new frames
   // Append the flowed frames to the principal child list; captions
@@ -8431,42 +8407,22 @@ nsCSSFrameConstructor::ContentRangeInser
     nsIFrame* appendAfterFrame;
     insertion.mParentFrame =
       ::AdjustAppendParentForAfterContent(this, container,
                                           frameItems.FirstChild()->GetParent(),
                                           aStartChild, &appendAfterFrame);
     prevSibling = ::FindAppendPrevSibling(insertion.mParentFrame, appendAfterFrame);
   }
 
-  bool dealtWithFirstLine = false;
-  if (haveFirstLineStyle && insertion.mParentFrame == containingBlock) {
+  if (haveFirstLineStyle && insertion.mParentFrame == containingBlock && isAppend) {
     // It's possible that the new frame goes into a first-line
     // frame. Look at it and see...
-    if (isAppend) {
-      // Use append logic when appending
-      AppendFirstLineFrames(state, containingBlock->GetContent(),
-                            containingBlock, frameItems);
-      // That moved things into line frames as needed, reparenting their
-      // styles.  Nothing else needs to be done to handle ::first-line.
-      dealtWithFirstLine = true;
-    }
-    else {
-      // Use more complicated insert logic when inserting
-      // XXXbz this method is a no-op, so it's easy for the args being passed
-      // here to make no sense without anyone noticing...  If it ever stops
-      // being a no-op, vet them carefully!
-      // XXXbz Can this code even get hit?  I'd think/hope not, since any
-      // insert would go into an existing lineframe if we have them..
-      InsertFirstLineFrames(state, container, containingBlock, &insertion.mParentFrame,
-                            prevSibling, frameItems);
-    }
-  }
-
-  if (!dealtWithFirstLine &&
-      insertion.mParentFrame->StyleContext()->HasPseudoElementData()) {
+    AppendFirstLineFrames(state, containingBlock->GetContent(),
+                          containingBlock, frameItems);
+  } else if (insertion.mParentFrame->StyleContext()->HasPseudoElementData()) {
     CheckForFirstLineInsertion(insertion.mParentFrame, frameItems);
     CheckForFirstLineInsertion(insertion.mParentFrame, captionItems);
   }
 
   // We might have captions; put them into the caption list of the
   // table wrapper frame.
   if (captionItems.NotEmpty()) {
     NS_ASSERTION(LayoutFrameType::Table == frameType ||
@@ -8541,18 +8497,17 @@ nsCSSFrameConstructor::ContentRangeInser
 #ifdef DEBUG
   if (gReallyNoisyContentUpdates && insertion.mParentFrame) {
     printf("nsCSSFrameConstructor::ContentRangeInserted: resulting frame model:\n");
     insertion.mParentFrame->List(stdout, 0);
   }
 #endif
 
 #ifdef ACCESSIBILITY
-  nsAccessibilityService* accService = nsIPresShell::AccService();
-  if (accService) {
+  if (nsAccessibilityService* accService = nsIPresShell::AccService()) {
     accService->ContentRangeInserted(mPresShell, aContainer,
                                      aStartChild, aEndChild);
   }
 #endif
 }
 
 bool
 nsCSSFrameConstructor::ContentRemoved(nsIContent* aContainer,
@@ -11486,159 +11441,16 @@ nsCSSFrameConstructor::AppendFirstLineFr
     return;
   }
 
   nsFirstLineFrame* lineFrame = static_cast<nsFirstLineFrame*>(lastBlockKid);
   WrapFramesInFirstLineFrame(aState, aBlockContent, aBlockFrame,
                              lineFrame, aFrameItems);
 }
 
-// Special routine to handle inserting a new frame into a block
-// frame's child list. Takes care of placing the new frame into the
-// right place when first-line style is present.
-void
-nsCSSFrameConstructor::InsertFirstLineFrames(
-  nsFrameConstructorState& aState,
-  nsIContent*              aContent,
-  nsIFrame*                aBlockFrame,
-  nsContainerFrame**       aParentFrame,
-  nsIFrame*                aPrevSibling,
-  nsFrameItems&            aFrameItems)
-{
-  // XXXbz If you make this method actually do something, check to
-  // make sure that the caller is passing what you expect.  In
-  // particular, which content is aContent?  And audit the rest of
-  // this code too; it makes bogus assumptions and may not build.
-#if 0
-  nsIFrame* parentFrame = *aParentFrame;
-  nsIFrame* newFrame = aFrameItems.childList;
-  bool isInline = IsInlineOutside(newFrame);
-
-  if (!aPrevSibling) {
-    // Insertion will become the first frame. Two cases: we either
-    // already have a first-line frame or we don't.
-    nsIFrame* firstBlockKid = aBlockFrame->PrincipalChildList().FirstChild();
-    if (firstBlockKid->IsLineFrame()) {
-      // We already have a first-line frame
-      nsIFrame* lineFrame = firstBlockKid;
-
-      if (isInline) {
-        // Easy case: the new inline frame will go into the lineFrame.
-        ReparentFrame(this, lineFrame, newFrame);
-        InsertFrames(lineFrame, kPrincipalList, nullptr, newFrame);
-
-        // Since the frame is going into the lineFrame, don't let it
-        // go into the block too.
-        aFrameItems.childList = nullptr;
-        aFrameItems.lastChild = nullptr;
-      }
-      else {
-        // Harder case: We are about to insert a block level element
-        // before the first-line frame.
-        // XXX need a method to steal away frames from the line-frame
-      }
-    }
-    else {
-      // We do not have a first-line frame
-      if (isInline) {
-        // We now need a first-line frame to contain the inline frame.
-        nsIFrame* lineFrame = NS_NewFirstLineFrame(firstLineStyle);
-
-        if (NS_SUCCEEDED(rv)) {
-          // Lookup first-line style context
-          nsStyleContext* parentStyle =
-            nsFrame::CorrectStyleParentFrame(aBlockFrame,
-                                             nsCSSPseudoElements::firstLine)->
-              StyleContext();
-          RefPtr<nsStyleContext> firstLineStyle =
-            GetFirstLineStyle(aContent, parentStyle);
-
-          // Initialize the line frame
-          InitAndRestoreFrame(aState, aContent, aBlockFrame, lineFrame);
-
-          // Make sure the caller inserts the lineFrame into the
-          // blocks list of children.
-          aFrameItems.childList = lineFrame;
-          aFrameItems.lastChild = lineFrame;
-
-          // Give the inline frames to the lineFrame <b>after</b>
-          // reparenting them
-          NS_ASSERTION(lineFrame->StyleContext() == firstLineStyle,
-                       "Bogus style context on line frame");
-          ReparentFrame(aPresContext, lineFrame, newFrame);
-          lineFrame->SetInitialChildList(kPrincipalList, newFrame);
-        }
-      }
-      else {
-        // Easy case: the regular insertion logic can insert the new
-        // frame because it's a block frame.
-      }
-    }
-  }
-  else {
-    // Insertion will not be the first frame.
-    nsIFrame* prevSiblingParent = aPrevSibling->GetParent();
-    if (prevSiblingParent == aBlockFrame) {
-      // Easy case: The prev-siblings parent is the block
-      // frame. Therefore the prev-sibling is not currently in a
-      // line-frame. Therefore the new frame which is going after it,
-      // regardless of type, is not going into a line-frame.
-    }
-    else {
-      // If the prevSiblingParent is not the block-frame then it must
-      // be a line-frame (if it were a letter-frame, that logic would
-      // already have adjusted the prev-sibling to be the
-      // letter-frame).
-      if (isInline) {
-        // Easy case: the insertion can go where the caller thinks it
-        // should go (which is into prevSiblingParent).
-      }
-      else {
-        // Block elements don't end up in line-frames, therefore
-        // change the insertion point to aBlockFrame. However, there
-        // might be more inline elements following aPrevSibling that
-        // need to be pulled out of the line-frame and become children
-        // of the block.
-        nsIFrame* nextSibling = aPrevSibling->GetNextSibling();
-        nsIFrame* nextLineFrame = prevSiblingParent->GetNextInFlow();
-        if (nextSibling || nextLineFrame) {
-          // Oy. We have work to do. Create a list of the new frames
-          // that are going into the block by stripping them away from
-          // the line-frame(s).
-          if (nextSibling) {
-            nsLineFrame* lineFrame = (nsLineFrame*) prevSiblingParent;
-            nsFrameList tail = lineFrame->StealFramesAfter(aPrevSibling);
-            // XXX do something with 'tail'
-          }
-
-          nsLineFrame* nextLineFrame = (nsLineFrame*) lineFrame;
-          for (;;) {
-            nextLineFrame = nextLineFrame->GetNextInFlow();
-            if (!nextLineFrame) {
-              break;
-            }
-            nsIFrame* kids = nextLineFrame->PrincipalChildList().FirstChild();
-          }
-        }
-        else {
-          // We got lucky: aPrevSibling was the last inline frame in
-          // the line-frame.
-          ReparentFrame(this, aBlockFrame, newFrame);
-          InsertFrames(aBlockFrame, kPrincipalList,
-                       prevSiblingParent, newFrame);
-          aFrameItems.childList = nullptr;
-          aFrameItems.lastChild = nullptr;
-        }
-      }
-    }
-  }
-
-#endif
-}
-
 void
 nsCSSFrameConstructor::CheckForFirstLineInsertion(nsIFrame* aParentFrame,
                                                   nsFrameItems& aFrameItems)
 {
   MOZ_ASSERT(aParentFrame->StyleContext()->HasPseudoElementData(),
              "Why were we called?");
 
   if (aFrameItems.IsEmpty()) {

--- a/layout/base/nsCSSFrameConstructor.h
+++ b/layout/base/nsCSSFrameConstructor.h
@@ -2096,23 +2096,16 @@ private:
 
   // Handle the case when a block with first-line style is appended to (by
   // possibly calling WrapFramesInFirstLineFrame as needed).
   void AppendFirstLineFrames(nsFrameConstructorState& aState,
                              nsIContent*              aContent,
                              nsContainerFrame*        aBlockFrame,
                              nsFrameItems&            aFrameItems);
 
-  void InsertFirstLineFrames(nsFrameConstructorState& aState,
-                             nsIContent*              aContent,
-                             nsIFrame*                aBlockFrame,
-                             nsContainerFrame**       aParentFrame,
-                             nsIFrame*                aPrevSibling,
-                             nsFrameItems&            aFrameItems);
-
   /**
    * When aFrameItems is being inserted into aParentFrame, and aParentFrame has
    * pseudo-element-affected styles, it's possible that we're inserting under a
    * ::first-line frame.  In that case, with servo's style system, the styles we
    * resolved for aFrameItems are wrong (they don't take ::first-line into
    * account), and we should fix them up, which is what this method does.
    *
    * This method does not mutate aFrameItems.

--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -1184,16 +1184,23 @@ nsDocumentViewer::PermitUnloadInternal(b
   if (!window) {
     // This is odd, but not fatal
     NS_WARNING("window not set for document!");
     return NS_OK;
   }
 
   NS_ASSERTION(nsContentUtils::IsSafeToRunScript(), "This is unsafe");
 
+  // https://html.spec.whatwg.org/multipage/browsing-the-web.html#prompt-to-unload-a-document
+  // Create an RAII object on mDocument that will increment the
+  // should-ignore-opens-during-unload counter on initialization
+  // and decrement it again when it goes out of score (regardless
+  // of how we exit this function).
+  IgnoreOpensDuringUnload ignoreOpens(mDocument);
+
   // Now, fire an BeforeUnload event to the document and see if it's ok
   // to unload...
   nsIPresShell* shell = mDocument->GetShell();
   nsPresContext* presContext = nullptr;
   if (shell) {
     presContext = shell->GetPresContext();
   }
   RefPtr<BeforeUnloadEvent> event =
@@ -1392,16 +1399,22 @@ nsDocumentViewer::PageHide(bool aIsUnloa
     nsPIDOMWindowOuter* window = mDocument->GetWindow();
 
     if (!window) {
       // Fail if no window is available...
       NS_WARNING("window not set for document!");
       return NS_ERROR_NULL_POINTER;
     }
 
+    // https://html.spec.whatwg.org/multipage/browsing-the-web.html#unload-a-document
+    // Create an RAII object on mDocument that will increment the
+    // should-ignore-opens-during-unload counter on initialization
+    // and decrement it again when it goes out of scope.
+    IgnoreOpensDuringUnload ignoreOpens(mDocument);
+
     // Now, fire an Unload event to the document...
     nsEventStatus status = nsEventStatus_eIgnore;
     WidgetEvent event(true, eUnload);
     event.mFlags.mBubbles = false;
     // XXX Dispatching to |window|, but using |document| as the target.
     event.mTarget = mDocument;
 
     // Never permit popups from the unload handler, no matter how we get

--- a/layout/generic/WritingModes.h
+++ b/layout/generic/WritingModes.h
@@ -1484,123 +1484,132 @@ private:
  */
 class LogicalRect {
 public:
   explicit LogicalRect(WritingMode aWritingMode)
     :
 #ifdef DEBUG
       mWritingMode(aWritingMode),
 #endif
-      mRect(0, 0, 0, 0)
+      mIStart(0),
+      mBStart(0),
+      mISize(0),
+      mBSize(0)
   { }
 
   LogicalRect(WritingMode aWritingMode,
               nscoord aIStart, nscoord aBStart,
               nscoord aISize, nscoord aBSize)
     :
 #ifdef DEBUG
       mWritingMode(aWritingMode),
 #endif
-      mRect(aIStart, aBStart, aISize, aBSize)
+      mIStart(aIStart),
+      mBStart(aBStart),
+      mISize(aISize),
+      mBSize(aBSize)
   { }
 
   LogicalRect(WritingMode aWritingMode,
               const LogicalPoint& aOrigin,
               const LogicalSize& aSize)
     :
 #ifdef DEBUG
       mWritingMode(aWritingMode),
 #endif
-      mRect(aOrigin.mPoint, aSize.mSize)
+      mIStart(aOrigin.mPoint.x),
+      mBStart(aOrigin.mPoint.y),
+      mISize(aSize.mSize.width),
+      mBSize(aSize.mSize.height)
   {
     CHECK_WRITING_MODE(aOrigin.GetWritingMode());
     CHECK_WRITING_MODE(aSize.GetWritingMode());
   }
 
   LogicalRect(WritingMode aWritingMode,
               const nsRect& aRect,
               const nsSize& aContainerSize)
 #ifdef DEBUG
     : mWritingMode(aWritingMode)
 #endif
   {
     if (aWritingMode.IsVertical()) {
-      mRect.y = aWritingMode.IsVerticalLR()
-                ? aRect.x : aContainerSize.width - aRect.XMost();
-      mRect.x = aWritingMode.IsInlineReversed()
-                ? aContainerSize.height - aRect.YMost() : aRect.y;
-      mRect.height = aRect.width;
-      mRect.width = aRect.height;
+      mBStart = aWritingMode.IsVerticalLR()
+               ? aRect.X() : aContainerSize.width - aRect.XMost();
+      mIStart = aWritingMode.IsInlineReversed()
+               ? aContainerSize.height - aRect.YMost() : aRect.Y();
+      mBSize = aRect.Width();
+      mISize = aRect.Height();
     } else {
-      mRect.x = aWritingMode.IsInlineReversed()
-                ? aContainerSize.width - aRect.XMost() : aRect.x;
-      mRect.y = aRect.y;
-      mRect.width = aRect.width;
-      mRect.height = aRect.height;
+      mIStart = aWritingMode.IsInlineReversed()
+               ? aContainerSize.width - aRect.XMost() : aRect.X();
+      mBStart = aRect.Y();
+      mISize = aRect.Width();
+      mBSize = aRect.Height();
     }
   }
 
   /**
    * Inline- and block-dimension geometry.
    */
   nscoord IStart(WritingMode aWritingMode) const // inline-start edge
   {
     CHECK_WRITING_MODE(aWritingMode);
-    return mRect.X();
+    return mIStart;
   }
   nscoord IEnd(WritingMode aWritingMode) const // inline-end edge
   {
     CHECK_WRITING_MODE(aWritingMode);
-    return mRect.XMost();
+    return mIStart + mISize;
   }
   nscoord ISize(WritingMode aWritingMode) const // inline-size
   {
     CHECK_WRITING_MODE(aWritingMode);
-    return mRect.Width();
+    return mISize;
   }
 
   nscoord BStart(WritingMode aWritingMode) const // block-start edge
   {
     CHECK_WRITING_MODE(aWritingMode);
-    return mRect.Y();
+    return mBStart;
   }
   nscoord BEnd(WritingMode aWritingMode) const // block-end edge
   {
     CHECK_WRITING_MODE(aWritingMode);
-    return mRect.YMost();
+    return mBStart + mBSize;
   }
   nscoord BSize(WritingMode aWritingMode) const // block-size
   {
     CHECK_WRITING_MODE(aWritingMode);
-    return mRect.Height();
+    return mBSize;
   }
 
   /**
    * Writable (reference) accessors are only available for the basic logical
    * fields (Start and Size), not derivatives like End.
    */
   nscoord& IStart(WritingMode aWritingMode) // inline-start edge
   {
     CHECK_WRITING_MODE(aWritingMode);
-    return mRect.x;
+    return mIStart;
   }
   nscoord& ISize(WritingMode aWritingMode) // inline-size
   {
     CHECK_WRITING_MODE(aWritingMode);
-    return mRect.width;
+    return mISize;
   }
   nscoord& BStart(WritingMode aWritingMode) // block-start edge
   {
     CHECK_WRITING_MODE(aWritingMode);
-    return mRect.y;
+    return mBStart;
   }
   nscoord& BSize(WritingMode aWritingMode) // block-size
   {
     CHECK_WRITING_MODE(aWritingMode);
-    return mRect.height;
+    return mBSize;
   }
 
   /**
    * Accessors for line-relative coordinates
    */
   nscoord LineLeft(WritingMode aWritingMode,
                    const nsSize& aContainerSize) const
   {
@@ -1627,91 +1636,98 @@ public:
   /**
    * Physical coordinates of the rect.
    */
   nscoord X(WritingMode aWritingMode, nscoord aContainerWidth) const
   {
     CHECK_WRITING_MODE(aWritingMode);
     if (aWritingMode.IsVertical()) {
       return aWritingMode.IsVerticalLR() ?
-             mRect.Y() : aContainerWidth - mRect.YMost();
+             mBStart : aContainerWidth - BEnd();
     } else {
       return aWritingMode.IsInlineReversed() ?
-             aContainerWidth - mRect.XMost() : mRect.X();
+             aContainerWidth - IEnd() : mIStart;
     }
   }
 
   nscoord Y(WritingMode aWritingMode, nscoord aContainerHeight) const
   {
     CHECK_WRITING_MODE(aWritingMode);
     if (aWritingMode.IsVertical()) {
-      return aWritingMode.IsInlineReversed() ? aContainerHeight - mRect.XMost()
-                                             : mRect.X();
+      return aWritingMode.IsInlineReversed() ? aContainerHeight - IEnd()
+                                             : mIStart;
     } else {
-      return mRect.Y();
+      return mBStart;
     }
   }
 
   nscoord Width(WritingMode aWritingMode) const
   {
     CHECK_WRITING_MODE(aWritingMode);
-    return aWritingMode.IsVertical() ? mRect.Height() : mRect.Width();
+    return aWritingMode.IsVertical() ? mBSize : mISize;
   }
 
   nscoord Height(WritingMode aWritingMode) const
   {
     CHECK_WRITING_MODE(aWritingMode);
-    return aWritingMode.IsVertical() ? mRect.Width() : mRect.Height();
+    return aWritingMode.IsVertical() ? mISize : mBSize;
   }
 
   nscoord XMost(WritingMode aWritingMode, nscoord aContainerWidth) const
   {
     CHECK_WRITING_MODE(aWritingMode);
     if (aWritingMode.IsVertical()) {
       return aWritingMode.IsVerticalLR() ?
-             mRect.YMost() : aContainerWidth - mRect.Y();
+             BEnd() : aContainerWidth - mBStart;
     } else {
       return aWritingMode.IsInlineReversed() ?
-             aContainerWidth - mRect.X() : mRect.XMost();
+             aContainerWidth - mIStart : IEnd();
     }
   }
 
   nscoord YMost(WritingMode aWritingMode, nscoord aContainerHeight) const
   {
     CHECK_WRITING_MODE(aWritingMode);
     if (aWritingMode.IsVertical()) {
-      return aWritingMode.IsInlineReversed() ? aContainerHeight - mRect.x
-                                             : mRect.XMost();
+      return aWritingMode.IsInlineReversed() ? aContainerHeight - mIStart
+                                             : IEnd();
     } else {
-      return mRect.YMost();
+      return mBStart;
     }
   }
 
   bool IsEmpty() const
   {
-    return mRect.IsEmpty();
+    return mISize <= 0 || mBSize << 0;
   }
 
   bool IsAllZero() const
   {
-    return (mRect.x == 0 && mRect.y == 0 &&
-            mRect.width == 0 && mRect.height == 0);
+    return (mIStart == 0 && mBStart == 0 &&
+            mISize == 0 && mBSize == 0);
   }
 
   bool IsZeroSize() const
   {
-    return (mRect.width == 0 && mRect.height == 0);
+    return (mISize == 0 && mBSize == 0);
   }
 
-  void SetEmpty() { mRect.SetEmpty(); }
+  void SetEmpty() { mISize = mBSize = 0; }
 
   bool IsEqualEdges(const LogicalRect aOther) const
   {
     CHECK_WRITING_MODE(aOther.GetWritingMode());
-    return mRect.IsEqualEdges(aOther.mRect);
+    bool result = mIStart == aOther.mIStart && mBStart == aOther.mBStart &&
+                  mISize == aOther.mISize && mBSize == aOther.mBSize;
+
+    // We want the same result as nsRect, so assert we get it.
+    MOZ_ASSERT(result == nsRect(mIStart, mBStart, mISize, mBSize).
+                           IsEqualEdges(nsRect(aOther.mIStart, aOther.mBStart,
+                                               aOther.mISize, aOther.mBSize)));
+    return result;
   }
 
   LogicalPoint Origin(WritingMode aWritingMode) const
   {
     CHECK_WRITING_MODE(aWritingMode);
     return LogicalPoint(aWritingMode, IStart(), BStart());
   }
   void SetOrigin(WritingMode aWritingMode, const LogicalPoint& aPoint)
@@ -1732,59 +1748,127 @@ public:
     return LogicalRect(GetWritingMode(),
                        IStart() + aPoint.I(), BStart() + aPoint.B(),
                        ISize(), BSize());
   }
 
   LogicalRect& operator+=(const LogicalPoint& aPoint)
   {
     CHECK_WRITING_MODE(aPoint.GetWritingMode());
-    mRect += aPoint.mPoint;
+    mIStart += aPoint.mPoint.x;
+    mBStart += aPoint.mPoint.y;
     return *this;
   }
 
   LogicalRect operator-(const LogicalPoint& aPoint) const
   {
     CHECK_WRITING_MODE(aPoint.GetWritingMode());
     return LogicalRect(GetWritingMode(),
                        IStart() - aPoint.I(), BStart() - aPoint.B(),
                        ISize(), BSize());
   }
 
   LogicalRect& operator-=(const LogicalPoint& aPoint)
   {
     CHECK_WRITING_MODE(aPoint.GetWritingMode());
-    mRect -= aPoint.mPoint;
+    mIStart -= aPoint.mPoint.x;
+    mBStart -= aPoint.mPoint.y;
     return *this;
   }
 
   void MoveBy(WritingMode aWritingMode, const LogicalPoint& aDelta)
   {
     CHECK_WRITING_MODE(aWritingMode);
     CHECK_WRITING_MODE(aDelta.GetWritingMode());
     IStart() += aDelta.I();
     BStart() += aDelta.B();
   }
 
-  void Inflate(nscoord aD) { mRect.Inflate(aD); }
-  void Inflate(nscoord aDI, nscoord aDB) { mRect.Inflate(aDI, aDB); }
+  void Inflate(nscoord aD)
+  {
+#ifdef DEBUG
+    // Compute using nsRect and assert the results match
+    nsRect rectDebug(mIStart, mBStart, mISize, mBSize);
+    rectDebug.Inflate(aD);
+#endif
+    mIStart -= aD;
+    mBStart -= aD;
+    mISize += 2 * aD;
+    mBSize += 2 * aD;
+    MOZ_ASSERT(rectDebug.IsEqualEdges(nsRect(mIStart, mBStart, mISize, mBSize)));
+  }
+  void Inflate(nscoord aDI, nscoord aDB)
+  {
+#ifdef DEBUG
+    // Compute using nsRect and assert the results match
+    nsRect rectDebug(mIStart, mBStart, mISize, mBSize);
+    rectDebug.Inflate(aDI, aDB);
+#endif
+    mIStart -= aDI;
+    mBStart -= aDB;
+    mISize += 2 * aDI;
+    mBSize += 2 * aDB;
+    MOZ_ASSERT(rectDebug.IsEqualEdges(nsRect(mIStart, mBStart, mISize, mBSize)));
+  }
   void Inflate(WritingMode aWritingMode, const LogicalMargin& aMargin)
   {
     CHECK_WRITING_MODE(aWritingMode);
     CHECK_WRITING_MODE(aMargin.GetWritingMode());
-    mRect.Inflate(aMargin.mMargin);
+#ifdef DEBUG
+    // Compute using nsRect and assert the results match
+    nsRect rectDebug(mIStart, mBStart, mISize, mBSize);
+    rectDebug.Inflate(aMargin.mMargin);
+#endif
+    mIStart -= aMargin.mMargin.left;
+    mBStart -= aMargin.mMargin.top;
+    mISize += aMargin.mMargin.LeftRight();
+    mBSize += aMargin.mMargin.TopBottom();
+    MOZ_ASSERT(rectDebug.IsEqualEdges(nsRect(mIStart, mBStart, mISize, mBSize)));
   }
 
-  void Deflate(nscoord aD) { mRect.Deflate(aD); }
-  void Deflate(nscoord aDI, nscoord aDB) { mRect.Deflate(aDI, aDB); }
+  void Deflate(nscoord aD)
+  {
+#ifdef DEBUG
+    // Compute using nsRect and assert the results match
+    nsRect rectDebug(mIStart, mBStart, mISize, mBSize);
+    rectDebug.Deflate(aD);
+#endif
+    mIStart += aD;
+    mBStart += aD;
+    mISize = std::max(0, mISize - 2 * aD);
+    mBSize = std::max(0, mBSize - 2 * aD);
+    MOZ_ASSERT(rectDebug.IsEqualEdges(nsRect(mIStart, mBStart, mISize, mBSize)));
+  }
+  void Deflate(nscoord aDI, nscoord aDB)
+  {
+#ifdef DEBUG
+    // Compute using nsRect and assert the results match
+    nsRect rectDebug(mIStart, mBStart, mISize, mBSize);
+    rectDebug.Deflate(aDI, aDB);
+#endif
+    mIStart += aDI;
+    mBStart += aDB;
+    mISize = std::max(0, mISize - 2 * aDI);
+    mBSize = std::max(0, mBSize - 2 * aDB);
+    MOZ_ASSERT(rectDebug.IsEqualEdges(nsRect(mIStart, mBStart, mISize, mBSize)));
+  }
   void Deflate(WritingMode aWritingMode, const LogicalMargin& aMargin)
   {
     CHECK_WRITING_MODE(aWritingMode);
     CHECK_WRITING_MODE(aMargin.GetWritingMode());
-    mRect.Deflate(aMargin.mMargin);
+#ifdef DEBUG
+    // Compute using nsRect and assert the results match
+    nsRect rectDebug(mIStart, mBStart, mISize, mBSize);
+    rectDebug.Deflate(aMargin.mMargin);
+#endif
+    mIStart += aMargin.mMargin.left;
+    mBStart += aMargin.mMargin.top;
+    mISize = std::max(0, mISize - aMargin.mMargin.LeftRight());
+    mBSize = std::max(0, mBSize - aMargin.mMargin.TopBottom());
+    MOZ_ASSERT(rectDebug.IsEqualEdges(nsRect(mIStart, mBStart, mISize, mBSize)));
   }
 
   /**
    * Return an nsRect containing our physical coordinates within the given
    * container size.
    */
   nsRect GetPhysicalRect(WritingMode aWritingMode,
                          const nsSize& aContainerSize) const
@@ -1818,75 +1902,102 @@ public:
   /**
    * Set *this to be the rectangle containing the intersection of aRect1
    * and aRect2, return whether the intersection is non-empty.
    */
   bool IntersectRect(const LogicalRect& aRect1, const LogicalRect& aRect2)
   {
     CHECK_WRITING_MODE(aRect1.mWritingMode);
     CHECK_WRITING_MODE(aRect2.mWritingMode);
-    return mRect.IntersectRect(aRect1.mRect, aRect2.mRect);
+#ifdef DEBUG
+    // Compute using nsRect and assert the results match
+    nsRect rectDebug;
+    rectDebug.IntersectRect(nsRect(aRect1.mIStart, aRect1.mBStart,
+                                   aRect1.mISize, aRect1.mBSize),
+                            nsRect(aRect2.mIStart, aRect2.mBStart,
+                                   aRect2.mISize, aRect2.mBSize));
+#endif
+
+    nscoord iEnd = std::min(aRect1.IEnd(), aRect2.IEnd());
+    mIStart = std::max(aRect1.mIStart, aRect2.mIStart);
+    mISize = iEnd - mIStart;
+
+    nscoord bEnd = std::min(aRect1.BEnd(), aRect2.BEnd());
+    mBStart = std::max(aRect1.mBStart, aRect2.mBStart);
+    mBSize = bEnd - mBStart;
+
+    if (mISize < 0 || mBSize < 0) {
+      mISize = 0;
+      mBSize = 0;
+    }
+
+    MOZ_ASSERT(rectDebug.IsEqualEdges(nsRect(mIStart, mBStart, mISize, mBSize)));
+    return mISize > 0 && mBSize > 0;
   }
 
 private:
   LogicalRect() = delete;
 
 #ifdef DEBUG
   WritingMode GetWritingMode() const { return mWritingMode; }
 #else
   WritingMode GetWritingMode() const { return WritingMode::Unknown(); }
 #endif
 
   nscoord IStart() const // inline-start edge
   {
-    return mRect.X();
+    return mIStart;
   }
   nscoord IEnd() const // inline-end edge
   {
-    return mRect.XMost();
+    return mIStart + mISize;
   }
   nscoord ISize() const // inline-size
   {
-    return mRect.Width();
+    return mISize;
   }
 
   nscoord BStart() const // block-start edge
   {
-    return mRect.Y();
+    return mBStart;
   }
   nscoord BEnd() const // block-end edge
   {
-    return mRect.YMost();
+    return mBStart + mBSize;
   }
   nscoord BSize() const // block-size
   {
-    return mRect.Height();
+    return mBSize;
   }
 
   nscoord& IStart() // inline-start edge
   {
-    return mRect.x;
+    return mIStart;
   }
   nscoord& ISize() // inline-size
   {
-    return mRect.width;
+    return mISize;
   }
   nscoord& BStart() // block-start edge
   {
-    return mRect.y;
+    return mBStart;
   }
   nscoord& BSize() // block-size
   {
-    return mRect.height;
+    return mBSize;
   }
 
 #ifdef DEBUG
   WritingMode mWritingMode;
 #endif
-  nsRect      mRect;
+  // Inline- and block-geometry dimension
+  nscoord     mIStart; // inline-start edge
+  nscoord     mBStart; // block-start edge
+  nscoord     mISize; // inline-size
+  nscoord     mBSize; // block-size
 };
 
 } // namespace mozilla
 
 // Definitions of inline methods for nsStyleSides, declared in nsStyleCoord.h
 // but not defined there because they need WritingMode.
 inline nsStyleUnit nsStyleSides::GetUnit(mozilla::WritingMode aWM,
                                          mozilla::LogicalSide aSide) const