--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -231,17 +231,16 @@ module.exports = {
       "dom/tests/mochitest/**",
       "dom/u2f/**",
       "dom/vr/**",
       "dom/webauthn/**",
       "dom/webgpu/**",
       "dom/websocket/**",
       "dom/workers/**",
       "dom/worklet/**",
-      "dom/xbl/**",
       "dom/xml/**",
       "dom/xslt/**",
       "dom/xul/**",
     ],
     "rules": {
       "consistent-return": "off",
       "mozilla/avoid-removeChild": "off",
       "mozilla/consistent-if-bracing": "off",

--- a/accessible/ipc/DocAccessibleParent.cpp
+++ b/accessible/ipc/DocAccessibleParent.cpp
@@ -134,27 +134,28 @@ uint32_t DocAccessibleParent::AddSubtree
     if (pending.mParentID == newChild.ID()) {
       if (!pending.mChildDoc->IsShutdown()) {
         AddChildDoc(pending.mChildDoc, pending.mParentID, false);
       }
       mPendingChildDocs.RemoveElementAt(index);
       break;
     }
   }
+  DebugOnly<bool> isOuterDoc = newProxy->ChildrenCount() == 1;
 
   uint32_t accessibles = 1;
   uint32_t kids = newChild.ChildrenCount();
   for (uint32_t i = 0; i < kids; i++) {
     uint32_t consumed = AddSubtree(newProxy, aNewTree, aIdx + accessibles, i);
     if (!consumed) return 0;
 
     accessibles += consumed;
   }
 
-  MOZ_ASSERT(newProxy->ChildrenCount() == kids);
+  MOZ_ASSERT((isOuterDoc && kids == 0) || newProxy->ChildrenCount() == kids);
 
   return accessibles;
 }
 
 mozilla::ipc::IPCResult DocAccessibleParent::RecvHideEvent(
     const uint64_t& aRootID, const bool& aFromUser) {
   if (mShutdown) return IPC_OK();
 

--- a/accessible/mac/Platform.mm
+++ b/accessible/mac/Platform.mm
@@ -53,18 +53,21 @@ void ProxyCreated(ProxyAccessible* aProx
     // will be a non-remote accessible.
     Accessible* outerDoc = aProxy->OuterDocOfRemoteBrowser();
     if (outerDoc) {
       nativeParent = GetNativeFromGeckoAccessible(outerDoc);
     }
   } else {
     // Non-top level proxies need proxy parents' children invalidated.
     ProxyAccessible* parent = aProxy->Parent();
-    nativeParent = GetNativeFromProxy(parent);
-    NS_ASSERTION(parent, "a non-top-level proxy is missing a parent?");
+    MOZ_ASSERT(parent ||
+                   // It's expected that an OOP iframe might not have a parent yet.
+                   (aProxy->IsDoc() && aProxy->AsDoc()->IsTopLevelInContentProcess()),
+               "a non-top-level proxy is missing a parent?");
+    nativeParent = parent ? GetNativeFromProxy(parent) : nullptr;
   }
 
   if (nativeParent) {
     [nativeParent invalidateChildren];
   }
 }
 
 void ProxyDestroyed(ProxyAccessible* aProxy) {
@@ -93,16 +96,31 @@ void ProxyDestroyed(ProxyAccessible* aPr
   aProxy->SetWrapper(0);
 
   if (nativeParent) {
     [nativeParent invalidateChildren];
   }
 }
 
 void ProxyEvent(ProxyAccessible* aProxy, uint32_t aEventType) {
+  if (aEventType == nsIAccessibleEvent::EVENT_REORDER && aProxy->ChildrenCount() == 1 &&
+      aProxy->ChildAt(0)->IsDoc()) {
+    // This is a remote OuterDocAccessible. The reorder event indicates that Its
+    // embedded document has been added or changed. If the document itself is
+    // an existing Accessible, ProxyCreated won't have been called, so we won't
+    // have invalidated native children. This can happen for in-process iframes
+    // if the OuterDocAccessible is re-created (e.g. due to layout reflow).
+    // It always happens for out-of-process iframes, as we must always call
+    // ProxyCreated before DocAccessibleParent::AddChildDoc for those.
+    mozAccessible* wrapper = GetNativeFromProxy(aProxy);
+    if (wrapper) {
+      [wrapper invalidateChildren];
+    }
+  }
+
   // ignore everything but focus-changed, value-changed, caret and selection
   // events for now.
   if (aEventType != nsIAccessibleEvent::EVENT_FOCUS &&
       aEventType != nsIAccessibleEvent::EVENT_VALUE_CHANGE &&
       aEventType != nsIAccessibleEvent::EVENT_TEXT_VALUE_CHANGE &&
       aEventType != nsIAccessibleEvent::EVENT_TEXT_CARET_MOVED &&
       aEventType != nsIAccessibleEvent::EVENT_TEXT_SELECTION_CHANGED)
     return;

--- a/browser/base/content/browser-siteProtections.js
+++ b/browser/base/content/browser-siteProtections.js
@@ -1231,28 +1231,40 @@ var gProtectionsHandler = {
     ));
   },
   get _protectionsPopupSiteNotWorkingTPSwitch() {
     delete this._protectionsPopupSiteNotWorkingTPSwitch;
     return (this._protectionsPopupSiteNotWorkingTPSwitch = document.getElementById(
       "protections-popup-siteNotWorking-tp-switch"
     ));
   },
+  get _protectionsPopupSiteNotWorkingReportError() {
+    delete this._protectionsPopupSiteNotWorkingReportError;
+    return (this._protectionsPopupSiteNotWorkingReportError = document.getElementById(
+      "protections-popup-sendReportView-report-error"
+    ));
+  },
   get _protectionsPopupSendReportLearnMore() {
     delete this._protectionsPopupSendReportLearnMore;
     return (this._protectionsPopupSendReportLearnMore = document.getElementById(
       "protections-popup-sendReportView-learn-more"
     ));
   },
   get _protectionsPopupSendReportURL() {
     delete this._protectionsPopupSendReportURL;
     return (this._protectionsPopupSendReportURL = document.getElementById(
       "protections-popup-sendReportView-collection-url"
     ));
   },
+  get _protectionsPopupSendReportButton() {
+    delete this._protectionsPopupSendReportButton;
+    return (this._protectionsPopupSendReportButton = document.getElementById(
+      "protections-popup-sendReportView-submit"
+    ));
+  },
   get _trackingProtectionIconTooltipLabel() {
     delete this._trackingProtectionIconTooltipLabel;
     return (this._trackingProtectionIconTooltipLabel = document.getElementById(
       "tracking-protection-icon-tooltip-label"
     ));
   },
 
   get noTrackersDetectedDescription() {
@@ -2169,17 +2181,22 @@ var gProtectionsHandler = {
   showSendReportView() {
     // Save this URI to make sure that the user really only submits the location
     // they see in the report breakage dialog.
     this.reportURI = gBrowser.currentURI;
     let urlWithoutQuery = this.reportURI.asciiSpec.replace(
       "?" + this.reportURI.query,
       ""
     );
+    let commentsTextarea = document.getElementById(
+      "protections-popup-sendReportView-collection-comments"
+    );
+    commentsTextarea.value = "";
     this._protectionsPopupSendReportURL.value = urlWithoutQuery;
+    this._protectionsPopupSiteNotWorkingReportError.hidden = true;
     this._protectionsPopupMultiView.showSubView(
       "protections-popup-sendReportView"
     );
   },
 
   toggleBreakageLink() {
     // The breakage link will only be shown if tracking protection is enabled
     // for the site and the TP toggle state is on. And we won't show the
@@ -2187,16 +2204,17 @@ var gProtectionsHandler = {
     // know the previous TP state. We check the ContentBlockingAllowList instead
     // of 'hasException' attribute of the protection popup for the previous
     // since the 'hasException' will also be toggled as well as toggling the TP
     // switch. We won't be able to know the previous TP state through the
     // 'hasException' attribute. So we fallback to check the
     // ContentBlockingAllowList here.
     this._protectionsPopupTPSwitchBreakageLink.hidden =
       ContentBlockingAllowList.includes(gBrowser.selectedBrowser) ||
+      !this._protectionsPopup.hasAttribute("blocking") ||
       !this._protectionsPopupTPSwitch.hasAttribute("enabled");
   },
 
   submitBreakageReport(uri) {
     let reportEndpoint = Services.prefs.getStringPref(
       this.PREF_REPORT_BREAKAGE_URL
     );
     if (!reportEndpoint) {
@@ -2264,38 +2282,41 @@ var gProtectionsHandler = {
         activatedBlockers.push(blocker.reportBreakageLabel);
       }
     }
 
     if (activatedBlockers.length) {
       formData.set("labels", activatedBlockers.join(","));
     }
 
+    this._protectionsPopupSendReportButton.disabled = true;
+
     fetch(reportEndpoint, {
       method: "POST",
       credentials: "omit",
       body: formData,
     })
-      .then(function(response) {
+      .then(response => {
+        this._protectionsPopupSendReportButton.disabled = false;
         if (!response.ok) {
           Cu.reportError(
             `Content Blocking report to ${reportEndpoint} failed with status ${
               response.status
             }`
           );
+          this._protectionsPopupSiteNotWorkingReportError.hidden = false;
         } else {
-          // Clear the textarea value when the report is submitted
-          commentsTextarea.value = "";
+          this._protectionsPopup.hidePopup();
+          ConfirmationHint.show(this.iconBox, "breakageReport");
         }
       })
       .catch(Cu.reportError);
   },
 
   onSendReportClicked() {
-    this._protectionsPopup.hidePopup();
     this.submitBreakageReport(this.reportURI);
   },
 
   async maybeUpdateEarliestRecordedDateTooltip() {
     if (this._hasEarliestRecord) {
       return;
     }
 

--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -3315,20 +3315,16 @@ function URLBarSetURI(aURI, updatePopupN
     gURLBar.selectionStart = gURLBar.selectionEnd = 0;
   }
 
   SetPageProxyState(valid ? "valid" : "invalid", updatePopupNotifications);
 }
 
 function losslessDecodeURI(aURI) {
   let scheme = aURI.scheme;
-  if (scheme == "moz-action") {
-    throw new Error("losslessDecodeURI should never get a moz-action URI");
-  }
-
   var value = aURI.displaySpec;
 
   let decodeASCIIOnly = !["https", "http", "file", "ftp"].includes(scheme);
   // Try to decode as UTF-8 if there's no encoding sequence that we would break.
   if (!/%25(?:3B|2F|3F|3A|40|26|3D|2B|24|2C|23)/i.test(value)) {
     if (decodeASCIIOnly) {
       // This only decodes ascii characters (hex) 20-7e, except 25 (%).
       // This avoids both cases stipulated below (%-related issues, and \r, \n

--- a/browser/base/content/browser.xhtml
+++ b/browser/base/content/browser.xhtml
@@ -72,16 +72,17 @@
         persist="screenX screenY width height sizemode"
         data-l10n-sync="true">
 
 <linkset>
   <html:link rel="localization" href="branding/brand.ftl"/>
   <html:link rel="localization" href="browser/branding/sync-brand.ftl"/>
   <html:link rel="localization" href="browser/browser.ftl"/>
   <html:link rel="localization" href="browser/menubar.ftl"/>
+  <html:link rel="localization" href="browser/protectionsPanel.ftl"/>
   <html:link rel="localization" href="browser/appmenu.ftl"/>
   <html:link rel="localization" href="browser/readerView.ftl"/>
 </linkset>
 
 # All JS files which are needed by browser.xhtml and other top level windows to
 # support MacOS specific features *must* go into the global-scripts.inc file so
 # that they can be shared with macWindow.inc.xul.
 #include global-scripts.inc

--- a/browser/base/content/test/siteProtections/browser.ini
+++ b/browser/base/content/test/siteProtections/browser.ini
@@ -1,6 +1,7 @@
 [DEFAULT]
 support-files =
   head.js
 
 [browser_protections_UI.js]
+skip-if = fission # Bug 1590696
 [browser_protections_UI_milestones.js]

--- a/browser/base/content/test/siteProtections/browser_protections_UI.js
+++ b/browser/base/content/test/siteProtections/browser_protections_UI.js
@@ -1,46 +1,57 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
 /* Basic UI tests for the protections panel */
 
+"use strict";
+
+const TRACKING_PAGE =
+  "http://tracking.example.org/browser/browser/base/content/test/trackingUI/trackingPage.html";
+
 ChromeUtils.defineModuleGetter(
   this,
   "ContentBlockingAllowList",
   "resource://gre/modules/ContentBlockingAllowList.jsm"
 );
 
 add_task(async function setup() {
   await SpecialPowers.pushPrefEnv({
     set: [
       // Set the auto hide timing to 100ms for blocking the test less.
       ["browser.protections_panel.toast.timeout", 100],
       // Hide protections cards so as not to trigger more async messaging
       // when landing on the page.
       ["browser.contentblocking.report.monitor.enabled", false],
       ["browser.contentblocking.report.lockwise.enabled", false],
       ["browser.contentblocking.report.proxy.enabled", false],
+      ["privacy.trackingprotection.enabled", true],
     ],
   });
   let oldCanRecord = Services.telemetry.canRecordExtended;
   Services.telemetry.canRecordExtended = true;
   Services.telemetry.clearEvents();
 
   registerCleanupFunction(() => {
     Services.telemetry.canRecordExtended = oldCanRecord;
     Services.telemetry.clearEvents();
   });
 });
 
 add_task(async function testToggleSwitch() {
   let tab = await BrowserTestUtils.openNewForegroundTab(
     gBrowser,
-    "https://example.com"
+    TRACKING_PAGE
   );
+
+  await TestUtils.waitForCondition(() => {
+    return gProtectionsHandler._protectionsPopup.hasAttribute("blocking");
+  });
+
   await openProtectionsPanel();
   let events = Services.telemetry.snapshotEvents(
     Ci.nsITelemetry.DATASET_PRERELEASE_CHANNELS
   ).parent;
   let buttonEvents = events.filter(
     e =>
       e[1] == "security.ui.protectionspopup" &&
       e[2] == "open" &&

--- a/browser/base/content/test/siteProtections/browser_protections_UI_milestones.js
+++ b/browser/base/content/test/siteProtections/browser_protections_UI_milestones.js
@@ -4,16 +4,17 @@
 add_task(async function setup() {
   await SpecialPowers.pushPrefEnv({
     set: [
       // Hide protections cards so as not to trigger more async messaging
       // when landing on the page.
       ["browser.contentblocking.report.monitor.enabled", false],
       ["browser.contentblocking.report.lockwise.enabled", false],
       ["browser.contentblocking.report.proxy.enabled", false],
+      ["browser.contentblocking.cfr-milestone.update-interval", 0],
     ],
   });
 });
 
 add_task(async function doTest() {
   // This also ensures that the DB tables have been initialized.
   await TrackingDBService.clearAll();
 

--- a/browser/base/content/test/tabs/browser.ini
+++ b/browser/base/content/test/tabs/browser.ini
@@ -64,18 +64,18 @@ skip-if = !e10s # Test only relevant for
 [browser_new_tab_insert_position.js]
 skip-if = (debug && os == 'linux' && bits == 32) #Bug 1455882, disabled on Linux32 for almost permafailing
 support-files = file_new_tab_page.html
 [browser_new_tab_in_privilegedabout_process_pref.js]
 skip-if = !e10s # Pref and test only relevant for e10s.
 [browser_privilegedmozilla_process_pref.js]
 skip-if = !e10s # Pref and test only relevant for e10s.
 [browser_new_web_tab_in_file_process_pref.js]
-fail-if = fission # Expects http tab opened from file to be loaded in file content process
 skip-if = !e10s # Pref and test only relevant for e10s.
+        || fission # Expects http tab opened from file to be loaded in file content process. See bug 1594221
 [browser_newwindow_tabstrip_overflow.js]
 [browser_open_newtab_start_observer_notification.js]
 [browser_opened_file_tab_navigated_to_web.js]
 [browser_overflowScroll.js]
 [browser_paste_event_at_middle_click_on_link.js]
 tags = clipboard
 support-files = file_anchor_elements.html
 [browser_pinnedTabs_clickOpen.js]

--- a/browser/base/content/test/trackingUI/browser_trackingUI_report_breakage.js
+++ b/browser/base/content/test/trackingUI/browser_trackingUI_report_breakage.js
@@ -59,16 +59,19 @@ add_task(async function setup() {
     ],
   });
 });
 
 add_task(async function testReportBreakageCancel() {
   Services.prefs.setBoolPref(TP_PREF, true);
 
   await BrowserTestUtils.withNewTab(TRACKING_PAGE, async function() {
+    await TestUtils.waitForCondition(() =>
+      gProtectionsHandler._protectionsPopup.hasAttribute("blocking")
+    );
     await openProtectionsPopup();
 
     let siteNotWorkingButton = document.getElementById(
       "protections-popup-tp-switch-breakage-link"
     );
     ok(
       BrowserTestUtils.is_visible(siteNotWorkingButton),
       "site not working button is visible"
@@ -103,16 +106,41 @@ add_task(async function testReportBreaka
     await viewShown;
 
     ok(true, "Main view was shown");
   });
 
   Services.prefs.clearUserPref(TP_PREF);
 });
 
+add_task(async function testNoTracking() {
+  await BrowserTestUtils.withNewTab(BENIGN_PAGE, async function() {
+    await openProtectionsPopup();
+
+    let siteNotWorkingButton = document.getElementById(
+      "protections-popup-tp-switch-breakage-link"
+    );
+    ok(
+      BrowserTestUtils.is_hidden(siteNotWorkingButton),
+      "site not working button is not visible"
+    );
+  });
+});
+
+add_task(async function testReportBreakageError() {
+  Services.prefs.setBoolPref(TP_PREF, true);
+  // Make sure that we correctly strip the query.
+  let url = TRACKING_PAGE + "?a=b&1=abc&unicode=🦊";
+  await BrowserTestUtils.withNewTab(url, async function() {
+    await testReportBreakage(TRACKING_PAGE, "trackingprotection", true);
+  });
+
+  Services.prefs.clearUserPref(TP_PREF);
+});
+
 add_task(async function testTP() {
   Services.prefs.setBoolPref(TP_PREF, true);
   // Make sure that we correctly strip the query.
   let url = TRACKING_PAGE + "?a=b&1=abc&unicode=🦊";
   await BrowserTestUtils.withNewTab(url, async function() {
     await testReportBreakage(TRACKING_PAGE, "trackingprotection");
   });
 
@@ -134,61 +162,68 @@ add_task(async function testCR() {
 });
 
 add_task(async function testFP() {
   Services.prefs.setIntPref(CB_PREF, Ci.nsICookieService.BEHAVIOR_ACCEPT);
   Services.prefs.setBoolPref(FP_PREF, true);
   // Make sure that we correctly strip the query.
   let url = TRACKING_PAGE + "?a=b&1=abc&unicode=🦊";
   await BrowserTestUtils.withNewTab(url, async function(browser) {
+    let promise = waitForContentBlockingEvent();
     await SpecialPowers.spawn(browser, [], function() {
       content.postMessage("fingerprinting", "*");
     });
+    await promise;
 
     await testReportBreakage(TRACKING_PAGE, "fingerprinting");
   });
 
   Services.prefs.clearUserPref(FP_PREF);
   Services.prefs.clearUserPref(CB_PREF);
 });
 
 add_task(async function testCM() {
   Services.prefs.setIntPref(CB_PREF, Ci.nsICookieService.BEHAVIOR_ACCEPT);
   Services.prefs.setBoolPref(CM_PREF, true);
   // Make sure that we correctly strip the query.
   let url = TRACKING_PAGE + "?a=b&1=abc&unicode=🦊";
   await BrowserTestUtils.withNewTab(url, async function(browser) {
+    let promise = waitForContentBlockingEvent();
     await SpecialPowers.spawn(browser, [], function() {
       content.postMessage("cryptomining", "*");
     });
+    await promise;
 
     await testReportBreakage(TRACKING_PAGE, "cryptomining");
   });
 
   Services.prefs.clearUserPref(CM_PREF);
   Services.prefs.clearUserPref(CB_PREF);
 });
 
-async function testReportBreakage(url, tags) {
+async function testReportBreakage(url, tags, error = false) {
   // Setup a mock server for receiving breakage reports.
   let server = new HttpServer();
   server.start(-1);
   let i = server.identity;
   let path =
     i.primaryScheme + "://" + i.primaryHost + ":" + i.primaryPort + "/";
 
   Services.prefs.setStringPref(PREF_REPORT_BREAKAGE_URL, path);
 
+  await TestUtils.waitForCondition(() =>
+    gProtectionsHandler._protectionsPopup.hasAttribute("blocking")
+  );
   await openProtectionsPopup();
 
   let siteNotWorkingButton = document.getElementById(
     "protections-popup-tp-switch-breakage-link"
   );
-  await TestUtils.waitForCondition(
-    () => BrowserTestUtils.is_visible(siteNotWorkingButton),
+  ok(
+    BrowserTestUtils.is_visible(siteNotWorkingButton),
     "site not working button is visible"
   );
   let siteNotWorkingView = document.getElementById(
     "protections-popup-siteNotWorkingView"
   );
   let viewShown = BrowserTestUtils.waitForEvent(
     siteNotWorkingView,
     "ViewShown"
@@ -276,22 +311,45 @@ async function testReportBreakage(url, t
             "This is a comment\r\n",
           'Content-Disposition: form-data; name="labels"\r\n\r\n' +
             `${tags}\r\n`,
           "",
         ],
         "Should send the correct form data"
       );
 
+      if (error) {
+        response.setStatusLine(request.httpVersion, 500, "Request failed");
+      } else {
+        response.setStatusLine(request.httpVersion, 201, "Entry created");
+      }
+
       resolve();
     });
 
     comments.value = "This is a comment";
     submitButton.click();
   });
 
+  let errorMessage = document.getElementById(
+    "protections-popup-sendReportView-report-error"
+  );
+  if (error) {
+    await BrowserTestUtils.waitForCondition(() =>
+      BrowserTestUtils.is_visible(errorMessage)
+    );
+    is(
+      comments.value,
+      "This is a comment",
+      "Comment not cleared in case of an error"
+    );
+    gProtectionsHandler._protectionsPopup.hidePopup();
+  } else {
+    ok(BrowserTestUtils.is_hidden(errorMessage), "Error message not shown");
+  }
+
   await popuphidden;
 
   // Stop the server.
   await new Promise(r => server.stop(r));
 
   Services.prefs.clearUserPref(PREF_REPORT_BREAKAGE_URL);
 }

--- a/browser/components/BrowserGlue.jsm
+++ b/browser/components/BrowserGlue.jsm
@@ -2108,17 +2108,25 @@ BrowserGlue.prototype = {
         "permissions.eventTelemetry.enabled",
         this._togglePermissionPromptTelemetry
       );
       this._togglePermissionPromptTelemetry();
     });
 
     // Begin listening for incoming push messages.
     Services.tm.idleDispatchToMainThread(() => {
-      PushService.wrappedJSObject.ensureReady();
+      try {
+        PushService.wrappedJSObject.ensureReady();
+      } catch (ex) {
+        // NS_ERROR_NOT_AVAILABLE will get thrown for the PushService getter
+        // if the PushService is disabled.
+        if (ex.result != Cr.NS_ERROR_NOT_AVAILABLE) {
+          throw ex;
+        }
+      }
     });
 
     Services.tm.idleDispatchToMainThread(() => {
       this._recordContentBlockingTelemetry();
     });
 
     Services.tm.idleDispatchToMainThread(() => {
       this._recordContentBlockerTelemetry();

--- a/browser/components/controlcenter/content/protectionsPanel.inc.xul
+++ b/browser/components/controlcenter/content/protectionsPanel.inc.xul
@@ -305,16 +305,19 @@
           <vbox class="protections-popup-sendReportView-collection-section">
             <label control="protections-popup-sendReportView-collection-url">&contentBlocking.breakageReportView.collection.url.label;</label>
             <html:input readonly="readonly" id="protections-popup-sendReportView-collection-url" aria-label="&contentBlocking.breakageReportView.collection.url.label;"/>
           </vbox>
           <vbox class="protections-popup-sendReportView-collection-section">
             <label control="protections-popup-sendReportView-collection-comments">&contentBlocking.breakageReportView2.collection.comments.label;</label>
             <html:textarea id="protections-popup-sendReportView-collection-comments" aria-label="&contentBlocking.breakageReportView2.collection.comments.label;"/>
           </vbox>
+          <label id="protections-popup-sendReportView-report-error"
+            data-l10n-id="protections-panel-sendreportview-error"
+            hidden="true" role="alert"></label>
         </vbox>
         <vbox id="protections-popup-sendReportView-footer"
               class="panel-footer">
           <button id="protections-popup-sendReportView-cancel"
                   label="&contentBlocking.breakageReportView.cancel.label;"
                   oncommand="gProtectionsHandler._protectionsPopupMultiView.goBack();"/>
           <button id="protections-popup-sendReportView-submit"
                   default="true"

--- a/browser/components/extensions/test/browser/browser.ini
+++ b/browser/components/extensions/test/browser/browser.ini
@@ -1,14 +1,18 @@
 [DEFAULT]
 tags = webextensions
 prefs =
     # We don't want to reset this at the end of the test, so that we don't have
     # to spawn a new extension child process for each test unit.
     dom.ipc.keepProcessesAlive.extension=1
+    # With Fission enabled, this directory spawns many child processes, which
+    # somehow results in frequent leaks and shutdown hangs. Reuse the content
+    # processes to avoid this.
+    dom.ipc.keepProcessesAlive.webIsolated.perOrigin=1
     dom.animations-api.core.enabled=true
     dom.animations-api.timelines.enabled=true
     plugin.load_flash_only=false
 support-files =
   head.js
   head_devtools.js
   file_inspectedwindow_reload_target.sjs
   silence.ogg

--- a/browser/components/newtab/content-src/asrouter/templates/FirstRun/FirstRun.jsx
+++ b/browser/components/newtab/content-src/asrouter/templates/FirstRun/FirstRun.jsx
@@ -17,22 +17,28 @@ export const FLUENT_FILES = [
   "browser/newtab/onboarding.ftl",
 ];
 
 export const helpers = {
   selectInterruptAndTriplets(message = {}, interruptCleared) {
     const hasInterrupt =
       interruptCleared === true ? false : Boolean(message.content);
     const hasTriplets = Boolean(message.bundle && message.bundle.length);
+    // Allow 1) falsy to not render a header 2) default welcome 3) custom header
+    const tripletsHeaderId =
+      message.tripletsHeaderId === undefined
+        ? "onboarding-welcome-header"
+        : message.tripletsHeaderId;
     const UTMTerm = message.utm_term || "";
     return {
       hasTriplets,
       hasInterrupt,
       interrupt: hasInterrupt ? message : null,
       triplets: hasTriplets ? message.bundle : null,
+      tripletsHeaderId,
       UTMTerm,
     };
   },
 
   addFluent(document) {
     FLUENT_FILES.forEach(file => {
       const link = document.head.appendChild(document.createElement("link"));
       link.href = file;
@@ -50,16 +56,17 @@ export class FirstRun extends React.Pure
     this.state = {
       prevMessage: undefined,
 
       hasInterrupt: false,
       hasTriplets: false,
 
       interrupt: undefined,
       triplets: undefined,
+      tripletsHeaderId: "",
 
       isInterruptVisible: false,
       isTripletsContainerVisible: false,
       isTripletsContentVisible: false,
 
       UTMTerm: "",
 
       flowParams: undefined,
@@ -82,28 +89,30 @@ export class FirstRun extends React.Pure
       interruptCleared !== state.prevInterruptCleared ||
       (message && message.id !== state.prevMessageId)
     ) {
       const {
         hasTriplets,
         hasInterrupt,
         interrupt,
         triplets,
+        tripletsHeaderId,
         UTMTerm,
       } = helpers.selectInterruptAndTriplets(message, interruptCleared);
 
       return {
         prevMessageId: message.id,
         prevInterruptCleared: interruptCleared,
 
         hasInterrupt,
         hasTriplets,
 
         interrupt,
         triplets,
+        tripletsHeaderId,
 
         isInterruptVisible: hasInterrupt,
         isTripletsContainerVisible: hasTriplets,
         isTripletsContentVisible: !(hasInterrupt || !hasTriplets),
 
         UTMTerm,
       };
     }
@@ -167,16 +176,17 @@ export class FirstRun extends React.Pure
       fxaEndpoint,
       dispatch,
       executeAction,
     } = props;
 
     const {
       interrupt,
       triplets,
+      tripletsHeaderId,
       isInterruptVisible,
       isTripletsContainerVisible,
       isTripletsContentVisible,
       hasTriplets,
       UTMTerm,
       flowParams,
     } = this.state;
 
@@ -196,16 +206,17 @@ export class FirstRun extends React.Pure
             onDismiss={this.closeInterrupt}
             fxaEndpoint={fxaEndpoint}
           />
         ) : null}
         {hasTriplets ? (
           <Triplets
             document={props.document}
             cards={triplets}
+            headerId={tripletsHeaderId}
             showCardPanel={isTripletsContainerVisible}
             showContent={isTripletsContentVisible}
             hideContainer={this.closeTriplets}
             sendUserActionTelemetry={sendUserActionTelemetry}
             UTMTerm={`${UTMTerm}-card`}
             flowParams={flowParams}
             onAction={executeAction}
           />

--- a/browser/components/newtab/content-src/asrouter/templates/FirstRun/Triplets.jsx
+++ b/browser/components/newtab/content-src/asrouter/templates/FirstRun/Triplets.jsx
@@ -50,26 +50,27 @@ export class Triplets extends React.Pure
       message_id: cards.map(m => m.id).join(","),
       action: "onboarding_user_event",
     });
   }
 
   render() {
     const {
       cards,
+      headerId,
       showCardPanel,
       showContent,
       sendUserActionTelemetry,
     } = this.props;
     return (
       <div
         className={`trailheadCards ${showCardPanel ? "expanded" : "collapsed"}`}
       >
         <div className="trailheadCardsInner" aria-hidden={!showContent}>
-          <h1 data-l10n-id="onboarding-welcome-header" />
+          {headerId && <h1 data-l10n-id={headerId} />}
           <div className={`trailheadCardGrid${showContent ? " show" : ""}`}>
             {cards.map(card => (
               <OnboardingCard
                 key={card.id}
                 className="trailheadCard"
                 sendUserActionTelemetry={sendUserActionTelemetry}
                 onAction={this.onCardAction}
                 UISurface="TRAILHEAD"

--- a/browser/components/newtab/data/content/activity-stream.bundle.js
+++ b/browser/components/newtab/data/content/activity-stream.bundle.js
@@ -3614,27 +3614,28 @@ class Triplets extends react__WEBPACK_IM
       message_id: cards.map(m => m.id).join(","),
       action: "onboarding_user_event"
     });
   }
 
   render() {
     const {
       cards,
+      headerId,
       showCardPanel,
       showContent,
       sendUserActionTelemetry
     } = this.props;
     return react__WEBPACK_IMPORTED_MODULE_0___default.a.createElement("div", {
       className: `trailheadCards ${showCardPanel ? "expanded" : "collapsed"}`
     }, react__WEBPACK_IMPORTED_MODULE_0___default.a.createElement("div", {
       className: "trailheadCardsInner",
       "aria-hidden": !showContent
-    }, react__WEBPACK_IMPORTED_MODULE_0___default.a.createElement("h1", {
-      "data-l10n-id": "onboarding-welcome-header"
+    }, headerId && react__WEBPACK_IMPORTED_MODULE_0___default.a.createElement("h1", {
+      "data-l10n-id": headerId
     }), react__WEBPACK_IMPORTED_MODULE_0___default.a.createElement("div", {
       className: `trailheadCardGrid${showContent ? " show" : ""}`
     }, cards.map(card => react__WEBPACK_IMPORTED_MODULE_0___default.a.createElement(_templates_OnboardingMessage_OnboardingMessage__WEBPACK_IMPORTED_MODULE_1__["OnboardingCard"], _extends({
       key: card.id,
       className: "trailheadCard",
       sendUserActionTelemetry: sendUserActionTelemetry,
       onAction: this.onCardAction,
       UISurface: "TRAILHEAD"
@@ -14692,22 +14693,24 @@ var addUtmParams = __webpack_require__(2
  // Note: should match the transition time on .trailheadCards in _Trailhead.scss
 
 const TRANSITION_LENGTH = 500;
 const FLUENT_FILES = ["branding/brand.ftl", "browser/branding/brandings.ftl", "browser/branding/sync-brand.ftl", "browser/newtab/onboarding.ftl"];
 const helpers = {
   selectInterruptAndTriplets(message = {}, interruptCleared) {
     const hasInterrupt = interruptCleared === true ? false : Boolean(message.content);
     const hasTriplets = Boolean(message.bundle && message.bundle.length);
+    const tripletsHeaderId = message.tripletsHeaderId === undefined ? "onboarding-welcome-header" : message.tripletsHeaderId;
     const UTMTerm = message.utm_term || "";
     return {
       hasTriplets,
       hasInterrupt,
       interrupt: hasInterrupt ? message : null,
       triplets: hasTriplets ? message.bundle : null,
+      tripletsHeaderId,
       UTMTerm
     };
   },
 
   addFluent(document) {
     FLUENT_FILES.forEach(file => {
       const link = document.head.appendChild(document.createElement("link"));
       link.href = file;
@@ -14721,16 +14724,17 @@ class FirstRun_FirstRun extends external
     super(props);
     this.didLoadFlowParams = false;
     this.state = {
       prevMessage: undefined,
       hasInterrupt: false,
       hasTriplets: false,
       interrupt: undefined,
       triplets: undefined,
+      tripletsHeaderId: "",
       isInterruptVisible: false,
       isTripletsContainerVisible: false,
       isTripletsContentVisible: false,
       UTMTerm: "",
       flowParams: undefined
     };
     this.closeInterrupt = this.closeInterrupt.bind(this);
     this.closeTriplets = this.closeTriplets.bind(this);
@@ -14749,25 +14753,27 @@ class FirstRun_FirstRun extends external
     } = props;
 
     if (interruptCleared !== state.prevInterruptCleared || message && message.id !== state.prevMessageId) {
       const {
         hasTriplets,
         hasInterrupt,
         interrupt,
         triplets,
+        tripletsHeaderId,
         UTMTerm
       } = helpers.selectInterruptAndTriplets(message, interruptCleared);
       return {
         prevMessageId: message.id,
         prevInterruptCleared: interruptCleared,
         hasInterrupt,
         hasTriplets,
         interrupt,
         triplets,
+        tripletsHeaderId,
         isInterruptVisible: hasInterrupt,
         isTripletsContainerVisible: hasTriplets,
         isTripletsContentVisible: !(hasInterrupt || !hasTriplets),
         UTMTerm
       };
     }
 
     return null;
@@ -14839,16 +14845,17 @@ class FirstRun_FirstRun extends external
       sendUserActionTelemetry,
       fxaEndpoint,
       dispatch,
       executeAction
     } = props;
     const {
       interrupt,
       triplets,
+      tripletsHeaderId,
       isInterruptVisible,
       isTripletsContainerVisible,
       isTripletsContentVisible,
       hasTriplets,
       UTMTerm,
       flowParams
     } = this.state;
     return external_React_default.a.createElement(external_React_default.a.Fragment, null, isInterruptVisible ? external_React_default.a.createElement(Interrupt_Interrupt, {
@@ -14861,16 +14868,17 @@ class FirstRun_FirstRun extends external
       executeAction: executeAction,
       dispatch: dispatch,
       flowParams: flowParams,
       onDismiss: this.closeInterrupt,
       fxaEndpoint: fxaEndpoint
     }) : null, hasTriplets ? external_React_default.a.createElement(Triplets["Triplets"], {
       document: props.document,
       cards: triplets,
+      headerId: tripletsHeaderId,
       showCardPanel: isTripletsContainerVisible,
       showContent: isTripletsContentVisible,
       hideContainer: this.closeTriplets,
       sendUserActionTelemetry: sendUserActionTelemetry,
       UTMTerm: `${UTMTerm}-card`,
       flowParams: flowParams,
       onAction: executeAction
     }) : null);

--- a/browser/components/newtab/lib/ASRouter.jsm
+++ b/browser/components/newtab/lib/ASRouter.jsm
@@ -1976,17 +1976,16 @@ class _ASRouter {
         lastMessageId: message ? message.id : null,
         messages: message
           ? state.messages.filter(m => m.id !== message.id)
           : state.messages,
       }));
     } else {
       // On new tab, send cards if they match; othwerise send a snippet
       message = await this.handleMessageRequest({
-        provider: "onboarding",
         template: "extended_triplets",
       });
 
       // Set up the experiment for extended triplets. It's done here because we
       // only want to enroll users (for both control and holdback) if they meet
       // the targeting criteria.
       if (message) {
         await this.setupExtendedTriplets();

--- a/browser/components/newtab/test/unit/asrouter/ASRouter.test.js
+++ b/browser/components/newtab/test/unit/asrouter/ASRouter.test.js
@@ -1383,17 +1383,16 @@ describe("ASRouter", () => {
       });
       it("should handle onboarding message provider", async () => {
         const handleMessageRequestStub = sandbox.stub(
           Router,
           "handleMessageRequest"
         );
         handleMessageRequestStub
           .withArgs({
-            provider: "onboarding",
             template: "extended_triplets",
           })
           .resolves({ id: "foo" });
         const spy = sandbox.spy(Router, "setupExtendedTriplets");
         const msg = fakeAsyncMessage({
           type: "NEWTAB_MESSAGE_REQUEST",
           data: {},
         });
@@ -1404,57 +1403,53 @@ describe("ASRouter", () => {
       it("should fallback to snippets if one was assigned to the holdback experiment", async () => {
         sandbox.stub(global.Sampling, "ratioSample").resolves(1); // 1 = holdback branch
         const handleMessageRequestStub = sandbox.stub(
           Router,
           "handleMessageRequest"
         );
         handleMessageRequestStub
           .withArgs({
-            provider: "onboarding",
             template: "extended_triplets",
           })
           .resolves({ id: "foo" });
         const msg = fakeAsyncMessage({
           type: "NEWTAB_MESSAGE_REQUEST",
           data: {},
         });
         await Router.onMessage(msg);
 
         assert.calledTwice(handleMessageRequestStub);
         assert.calledWithExactly(handleMessageRequestStub, {
-          provider: "onboarding",
           template: "extended_triplets",
         });
         assert.calledWithExactly(handleMessageRequestStub, {
           provider: "snippets",
         });
       });
       it("should fallback to snippets if onboarding message provider returned none", async () => {
         const handleMessageRequestStub = sandbox.stub(
           Router,
           "handleMessageRequest"
         );
         handleMessageRequestStub
           .withArgs({
-            provider: "onboarding",
             template: "extended_triplets",
           })
           .resolves(null);
         const spy = sandbox.spy(Router, "setupExtendedTriplets");
         const msg = fakeAsyncMessage({
           type: "NEWTAB_MESSAGE_REQUEST",
           data: {},
         });
         await Router.onMessage(msg);
 
         assert.notCalled(spy);
         assert.calledTwice(handleMessageRequestStub);
         assert.calledWithExactly(handleMessageRequestStub, {
-          provider: "onboarding",
           template: "extended_triplets",
         });
         assert.calledWithExactly(handleMessageRequestStub, {
           provider: "snippets",
         });
       });
     });
 

--- a/browser/components/privatebrowsing/test/browser/browser.ini
+++ b/browser/components/privatebrowsing/test/browser/browser.ini
@@ -24,17 +24,16 @@ support-files =
 skip-if = fission || verify
 tags = trackingprotection
 [browser_privatebrowsing_about_search_banner.js]
 [browser_privatebrowsing_aboutSessionRestore.js]
 [browser_privatebrowsing_cache.js]
 [browser_privatebrowsing_certexceptionsui.js]
 [browser_privatebrowsing_concurrent.js]
 [browser_privatebrowsing_context_and_chromeFlags.js]
-skip-if = fission
 [browser_privatebrowsing_crh.js]
 [browser_privatebrowsing_downloadLastDir.js]
 skip-if = verify
 [browser_privatebrowsing_downloadLastDir_c.js]
 [browser_privatebrowsing_downloadLastDir_toggle.js]
 [browser_privatebrowsing_favicon.js]
 [browser_privatebrowsing_geoprompt.js]
 tags = geolocation

--- a/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_context_and_chromeFlags.js
+++ b/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_context_and_chromeFlags.js
@@ -49,17 +49,19 @@ function assertWindowIsPrivate(win) {
  * window.
  */
 add_task(async function test_context_and_chromeFlags() {
   let win = await BrowserTestUtils.openNewBrowserWindow({ private: true });
   await assertWindowIsPrivate(win);
 
   let browser = win.gBrowser.selectedBrowser;
 
-  let newWinPromise = BrowserTestUtils.waitForNewWindow();
+  let newWinPromise = BrowserTestUtils.waitForNewWindow({
+    url: "http://example.com/",
+  });
   await ContentTask.spawn(browser, null, async function() {
     content.open("http://example.com", "_blank", "width=100,height=100");
   });
 
   let win2 = await newWinPromise;
   await assertWindowIsPrivate(win2);
 
   await BrowserTestUtils.closeWindow(win2);

--- a/browser/components/urlbar/tests/browser/browser.ini
+++ b/browser/components/urlbar/tests/browser/browser.ini
@@ -44,17 +44,16 @@ skip-if = verify && os == 'linux' # Bug 
 [browser_doubleClickSelectsAll.js]
 [browser_downArrowKeySearch.js]
 [browser_dragdropURL.js]
 [browser_dropmarker.js]
 [browser_ime_composition.js]
 [browser_inputHistory.js]
 [browser_inputHistory_emptystring.js]
 [browser_keepStateAcrossTabSwitches.js]
-skip-if = fission
 [browser_keywordBookmarklets.js]
 [browser_keyword_override.js]
 [browser_keywordSearch.js]
 support-files =
   searchSuggestionEngine.xml
   searchSuggestionEngine.sjs
 [browser_keywordSearch_postData.js]
 support-files =
@@ -64,18 +63,16 @@ support-files =
 [browser_keyword.js]
 support-files =
   print_postdata.sjs
   searchSuggestionEngine.xml
   searchSuggestionEngine.sjs
 [browser_locationBarCommand.js]
 skip-if = (os == 'mac' && os_version == '10.14') # bug 1554807
 [browser_locationBarExternalLoad.js]
-[browser_moz_action_link.js]
-skip-if = fission # Timeouts
 [browser_new_tab_urlbar_reset.js]
 [browser_openViewOnFocus.js]
 [browser_pasteAndGo.js]
 tags = clipboard
 [browser_percent_encoded.js]
 [browser_populateAfterPushState.js]
 [browser_primary_selection_safe_on_new_tab.js]
 [browser_privateBrowsingWindowChange.js]

--- a/browser/components/urlbar/tests/browser/browser_keepStateAcrossTabSwitches.js
+++ b/browser/components/urlbar/tests/browser/browser_keepStateAcrossTabSwitches.js
@@ -2,48 +2,47 @@
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
 "use strict";
 
 /**
  * Verify user typed text remains in the URL bar when tab switching, even when
  * loads fail.
  */
-add_task(async function() {
+add_task(async function validURL() {
   let input = "i-definitely-dont-exist.example.com";
   let tab = await BrowserTestUtils.openNewForegroundTab(
     gBrowser,
-    "about:blank",
-    false
+    "http://example.com/"
   );
   let browser = tab.linkedBrowser;
   // Note: Waiting on content document not being hidden because new tab pages can be preloaded,
   // in which case no load events fire.
   await ContentTask.spawn(browser, null, async () => {
     await ContentTaskUtils.waitForCondition(() => {
       return content.document && !content.document.hidden;
     });
   });
-  let errorPageLoaded = BrowserTestUtils.waitForErrorPage(tab.linkedBrowser);
+  let errorPageLoaded = BrowserTestUtils.waitForErrorPage(browser);
   gURLBar.value = input;
   gURLBar.select();
   EventUtils.sendKey("return");
   await errorPageLoaded;
   is(gURLBar.value, input, "Text is still in URL bar");
   await BrowserTestUtils.switchTab(gBrowser, tab.previousElementSibling);
   await BrowserTestUtils.switchTab(gBrowser, tab);
   is(gURLBar.value, input, "Text is still in URL bar after tab switch");
   BrowserTestUtils.removeTab(tab);
 });
 
 /**
  * Invalid URIs fail differently (that is, immediately, in the loadURI call)
  * if keyword searches are turned off. Test that this works, too.
  */
-add_task(async function() {
+add_task(async function invalidURL() {
   let input = "To be or not to be-that is the question";
   await SpecialPowers.pushPrefEnv({ set: [["keyword.enabled", false]] });
   let tab = await BrowserTestUtils.openNewForegroundTab(
     gBrowser,
     "about:blank",
     false
   );
   let browser = tab.linkedBrowser;

deleted file mode 100644
--- a/browser/components/urlbar/tests/browser/browser_moz_action_link.js
+++ /dev/null
@@ -1,40 +0,0 @@
-"use strict";
-
-const kURIs = ["moz-action:foo,", "moz-action:foo"];
-
-add_task(async function() {
-  for (let uri of kURIs) {
-    let dataURI = `data:text/html,<a id=a href="${uri}" target=_blank rel="opener">Link</a>`;
-    let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, dataURI);
-
-    let tabSwitchPromise = BrowserTestUtils.switchTab(gBrowser, function() {});
-    await ContentTask.spawn(tab.linkedBrowser, null, async function() {
-      content.document.getElementById("a").click();
-    });
-    await tabSwitchPromise;
-    isnot(gBrowser.selectedTab, tab, "Switched to new tab!");
-    is(
-      gURLBar.value,
-      "about:blank",
-      "URL bar should be displaying about:blank"
-    );
-    let newTab = gBrowser.selectedTab;
-    await BrowserTestUtils.switchTab(gBrowser, tab);
-    await BrowserTestUtils.switchTab(gBrowser, newTab);
-    is(gBrowser.selectedTab, newTab, "Switched to new tab again!");
-    is(
-      gURLBar.value,
-      "about:blank",
-      "URL bar should be displaying about:blank after tab switch"
-    );
-    // Finally, check that directly setting it produces the right results, too:
-    URLBarSetURI(makeURI(uri));
-    is(
-      gURLBar.value,
-      "about:blank",
-      "URL bar should still be displaying about:blank"
-    );
-    BrowserTestUtils.removeTab(newTab);
-    BrowserTestUtils.removeTab(tab);
-  }
-});

--- a/browser/components/urlbar/tests/browser/browser_urlbarDecode.js
+++ b/browser/components/urlbar/tests/browser/browser_urlbarDecode.js
@@ -49,18 +49,17 @@ add_task(function losslessDecode() {
 
 add_task(async function actionURILosslessDecode() {
   let urlNoScheme = "example.com/\u30a2\u30a4\u30a6\u30a8\u30aa";
   let url = "http://" + urlNoScheme;
   await promiseAutocompleteResultPopup(url);
 
   // At this point the heuristic result is selected but the urlbar's value is
   // simply `url`.  Key down and back around until the heuristic result is
-  // selected again, and at that point the urlbar's value should be a visiturl
-  // moz-action.
+  // selected again.
   do {
     EventUtils.synthesizeKey("KEY_ArrowDown");
   } while (UrlbarTestUtils.getSelectedRowIndex(window) != 0);
 
   let result = await UrlbarTestUtils.getDetailsOfResultAt(window, 0);
 
   Assert.equal(
     result.type,

--- a/browser/locales/en-US/browser/preferences/preferences.ftl
+++ b/browser/locales/en-US/browser/preferences/preferences.ftl
@@ -863,32 +863,36 @@ sync-device-name-save =
     .accesskey = v
 
 sync-connect-another-device = Connect another device
 
 ## Privacy Section
 
 privacy-header = Browser Privacy
 
-## Privacy Section - Forms
+## Privacy Section - Logins and Passwords
 
 logins-header = Logins and Passwords
+
+# Checkbox to control whether UI is shown to users to save or fill logins/passwords.
 forms-ask-to-save-logins =
     .label = Ask to save logins and passwords for websites
     .accesskey = r
 forms-exceptions =
     .label = Exceptions…
     .accesskey = x
 forms-generate-passwords =
     .label = Suggest and generate strong passwords
     .accesskey = u
 forms-breach-alerts =
     .label = Show alerts about passwords for breached websites
     .accesskey = b
 forms-breach-alerts-learn-more-link = Learn more
+
+# Checkbox which controls filling saved logins into fields automatically when they appear, in some cases without user interaction.
 forms-fill-logins-and-passwords =
     .label = Autofill logins and passwords
     .accesskey = i
 forms-saved-logins =
     .label = Saved Logins…
     .accesskey = L
 forms-master-pw-use =
     .label = Use a master password

new file mode 100644
--- /dev/null
+++ b/browser/locales/en-US/browser/protectionsPanel.ftl
@@ -0,0 +1,5 @@
+# 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/.
+
+protections-panel-sendreportview-error = There was an error sending the report. Please try again later.

--- a/browser/locales/en-US/chrome/browser/browser.properties
+++ b/browser/locales/en-US/chrome/browser/browser.properties
@@ -1015,13 +1015,14 @@ storageAccess.description.learnmore = th
 
 confirmationHint.sendToDevice.label = Sent!
 confirmationHint.copyURL.label = Copied to clipboard!
 confirmationHint.pageBookmarked.label = Saved to Library!
 confirmationHint.addSearchEngine.label = Search engine added!
 confirmationHint.pinTab.label = Pinned!
 confirmationHint.pinTab.description = Right-click the tab to unpin it.
 confirmationHint.passwordSaved.label = Password saved!
+confirmationHint.breakageReport.label = Report sent. Thank you!
 
 # LOCALIZATION NOTE (livebookmarkMigration.title):
 # Used by the export of user's live bookmarks to an OPML file as a title for the file.
 # %S will be replaced with brandShortName
 livebookmarkMigration.title                      = %S Live Bookmarks

--- a/browser/themes/shared/controlcenter/panel.inc.css
+++ b/browser/themes/shared/controlcenter/panel.inc.css
@@ -474,16 +474,21 @@ description#identity-popup-content-verif
 #protections-popup-sendReportView-collection-comments {
   height: 120px;
 }
 
 #protections-popup-sendReportView label {
   margin-inline-start: 0;
 }
 
+#protections-popup-sendReportView-report-error {
+  margin-bottom: 24px;
+  color: #d74345;
+}
+
 .protections-popup-category {
   /* Overwrite toolbarbutton styles */
   -moz-appearance: none;
   margin: 0;
   padding-inline-start: 0;
 }
 
 .protections-popup-category:-moz-focusring,

--- a/browser/themes/shared/urlbar-autocomplete.inc.css
+++ b/browser/themes/shared/urlbar-autocomplete.inc.css
@@ -124,19 +124,24 @@
   white-space: nowrap;
 }
 
 .urlbarView:not(.megabar) .urlbarView-results {
   padding-inline: @urlbarViewPadding@;
 }
 
 .urlbarView-row {
-  border-radius: 2px;
   fill: currentColor;
   fill-opacity: .6;
+  padding-block: 3px;
+}
+
+.urlbarView:not(.megabar) .urlbarView-row,
+.urlbarView.megabar .urlbarView-row-inner {
+  border-radius: 2px;
   padding-block: 6px;
   padding-inline-start: calc(@urlbarViewItemPaddingStart@);
 }
 
 .urlbarView:not(.megabar) .urlbarView-row {
   padding-inline-start: calc(var(--item-padding-start, calc(5px + @urlbarViewFaviconOffset@)) - @urlbarViewFaviconOffset@);
   padding-inline-end: var(--item-padding-end, 5px);
 }
@@ -161,21 +166,23 @@
   mask-image: linear-gradient(to right, transparent, black 2em);
 }
 
 .urlbarView-title[isurl]:-moz-locale-dir(rtl),
 .urlbarView-url:-moz-locale-dir(rtl) {
   direction: ltr !important;
 }
 
-.urlbarView-row:not([type=tip]):hover {
+.urlbarView:not(.megabar) .urlbarView-row:not([type=tip]):hover,
+.urlbarView.megabar .urlbarView-row:not([type=tip]):hover > .urlbarView-row-inner {
   background: var(--arrowpanel-dimmed);
 }
 
-.urlbarView-row:not([type=tip])[selected] {
+.urlbarView:not(.megabar) .urlbarView-row:not([type=tip])[selected],
+.urlbarView.megabar .urlbarView-row:not([type=tip])[selected] > .urlbarView-row-inner {
   background: var(--autocomplete-popup-highlight-background);
   color: var(--autocomplete-popup-highlight-color);
   fill-opacity: 1;
 }
 
 .urlbarView-type-icon,
 .urlbarView-favicon {
   min-width: 16px;

--- a/build/unix/mozconfig.unix
+++ b/build/unix/mozconfig.unix
@@ -8,17 +8,22 @@ if [ -n "$FORCE_GCC" ]; then
 
     # We want to make sure we use binutils and other binaries in the tooltool
     # package.
     mk_add_options "export PATH=$MOZ_FETCHES_DIR/gcc/bin:$PATH"
     ac_add_options --with-clang-path=$MOZ_FETCHES_DIR/clang/bin/clang
 else
     CC="$MOZ_FETCHES_DIR/clang/bin/clang"
     CXX="$MOZ_FETCHES_DIR/clang/bin/clang++"
-    export ENABLE_CLANG_PLUGIN=1
+
+    # For some builds we don't want to have Clang based static-analysis activated
+    if [ -z "$DISABLE_CLANG_PLUGIN" ]; then
+        export ENABLE_CLANG_PLUGIN=1
+    fi
+
     case "$PERFHERDER_EXTRA_OPTIONS" in
     base-toolchains*)
       # Clang versions < 7.0 don't support the -fcrash-diagnostics-dir flag.
       ;;
     *)
       export CFLAGS="$CFLAGS -fcrash-diagnostics-dir=${UPLOAD_PATH}"
       export CXXFLAGS="$CXXFLAGS -fcrash-diagnostics-dir=${UPLOAD_PATH}"
       ;;

--- a/devtools/client/debugger/src/actions/navigation.js
+++ b/devtools/client/debugger/src/actions/navigation.js
@@ -73,12 +73,13 @@ export function connect(
   };
 }
 
 /**
  * @memberof actions/navigation
  * @static
  */
 export function navigated() {
-  return async function({ panel }: ThunkArgs) {
+  return async function({ dispatch, panel }: ThunkArgs) {
+    await dispatch(updateThreads());
     panel.emit("reloaded");
   };
 }

--- a/devtools/client/debugger/src/actions/threads.js
+++ b/devtools/client/debugger/src/actions/threads.js
@@ -3,18 +3,24 @@
  * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
 
 // @flow
 
 import { differenceBy } from "lodash";
 import type { Action, ThunkArgs } from "./types";
 import type { ThreadType } from "../types";
 import { removeSourceActors } from "./source-actors";
+import { newGeneratedSources } from "./sources";
 
-import { getContext, getThreads, getSourceActorsForThread } from "../selectors";
+import {
+  getContext,
+  getAllThreads,
+  getThreads,
+  getSourceActorsForThread,
+} from "../selectors";
 
 export function updateThreads(type: ?ThreadType) {
   return async function({ dispatch, getState, client }: ThunkArgs) {
     const cx = getContext(getState());
     const threads = await client.fetchThreads(type);
 
     const currentThreads = getThreads(getState());
 
@@ -31,11 +37,32 @@ export function updateThreads(type: ?Thr
           type: "REMOVE_THREADS",
           cx,
           threads: removedThreads.map(t => t.actor),
         }: Action)
       );
     }
     if (addedThreads.length > 0) {
       dispatch(({ type: "INSERT_THREADS", cx, threads: addedThreads }: Action));
+
+      // Fetch the sources and install breakpoints on any new workers.
+      // NOTE: This runs in the background and fails quietly because it is
+      // pretty easy for sources to throw during the fetch if their thread
+      // shuts down, which would cause test failures.
+      for (const thread of addedThreads) {
+        client
+          .fetchThreadSources(thread.actor)
+          .then(sources => dispatch(newGeneratedSources(sources)))
+          .catch(e => console.error(e));
+      }
     }
   };
 }
+
+export function ensureHasThread(thread: string) {
+  return async function({ dispatch, getState, client }: ThunkArgs) {
+    const currentThreads = getAllThreads(getState());
+    if (!currentThreads.some(t => t.actor == thread)) {
+      await dispatch(updateThreads("worker"));
+      await dispatch(updateThreads("contentProcess"));
+    }
+  };
+}

--- a/devtools/client/debugger/src/client/firefox/commands.js
+++ b/devtools/client/debugger/src/client/firefox/commands.js
@@ -310,20 +310,22 @@ function autocomplete(
       cursor,
       result => resolve(result),
       frameId
     );
   });
 }
 
 function navigate(url: string): Promise<*> {
+  targets = { worker: {}, contentProcess: {} };
   return currentTarget.navigateTo({ url });
 }
 
 function reload(): Promise<*> {
+  targets = { worker: {}, contentProcess: {} };
   return currentTarget.reload();
 }
 
 function getProperties(thread: string, grip: Grip): Promise<*> {
   const objClient = lookupThreadFront(thread).pauseGrip(grip);
 
   return objClient.getPrototypeAndProperties().then(resp => {
     const { ownProperties, safeGetterValues } = resp;
@@ -442,16 +444,22 @@ function getAllThreadFronts() {
 async function fetchSources(): Promise<Array<GeneratedSourceData>> {
   let sources = [];
   for (const threadFront of getAllThreadFronts()) {
     sources = sources.concat(await getSources(threadFront));
   }
   return sources;
 }
 
+async function fetchThreadSources(
+  thread: string
+): Promise<Array<GeneratedSourceData>> {
+  return getSources(lookupThreadFront(thread));
+}
+
 // Check if any of the targets were paused before we opened
 // the debugger. If one is paused. Fake a `pause` RDP event
 // by directly calling the client event listener.
 async function checkIfAlreadyPaused() {
   for (const threadFront of getAllThreadFronts()) {
     const pausedPacket = threadFront.getLastPausePacket();
     if (pausedPacket) {
       clientEvents.paused(threadFront, pausedPacket);
@@ -478,36 +486,23 @@ async function fetchThreads(type: ?Threa
 
 async function updateThreads(type: ThreadType) {
   const options = {
     breakpoints,
     eventBreakpoints,
     observeAsmJS: true,
   };
 
-  const oldActors = Object.keys(targets[type]);
-
   await updateTargets(type, {
     currentTarget,
     debuggerClient,
     targets,
     options,
   });
 
-  // Fetch the sources and install breakpoints on any new workers.
-  // NOTE: This runs in the background and fails quitely because it is
-  // pretty easy for sources to throw during the fetch if their thread
-  // shuts down, which would cause test failures.
-  for (const entry of Object.entries(targets[type])) {
-    const [actor, { threadFront }] = (entry: any);
-    if (!oldActors.includes(actor)) {
-      getSources(threadFront).catch(e => console.error(e));
-    }
-  }
-
   return Object.entries(targets[type]).map(([actor, target]) =>
     createThread((actor: any), (target: any))
   );
 }
 
 function getMainThread() {
   return currentThreadFront.actor;
 }
@@ -591,16 +586,17 @@ const clientCommands = {
   evaluateExpressions,
   navigate,
   reload,
   getProperties,
   getFrameScopes,
   pauseOnExceptions,
   toggleEventLogging,
   fetchSources,
+  fetchThreadSources,
   checkIfAlreadyPaused,
   registerSourceActor,
   fetchThreads,
   getMainThread,
   sendPacket,
   setSkipPausing,
   setEventListenerBreakpoints,
   getEventListenerBreakpointTypes,

--- a/devtools/client/debugger/src/client/firefox/events.js
+++ b/devtools/client/debugger/src/client/firefox/events.js
@@ -11,16 +11,22 @@ import type {
   Actions,
   Target,
   DebuggerClient,
 } from "./types";
 
 import { createPause, prepareSourcePayload } from "./create";
 import sourceQueue from "../../utils/source-queue";
 import { recordEvent } from "../../utils/telemetry";
+import { features } from "../../utils/prefs";
+
+const {
+  WorkersListener,
+  // $FlowIgnore
+} = require("devtools/client/shared/workers-listener.js");
 
 const CALL_STACK_PAGE_SIZE = 1000;
 
 type Dependencies = {
   threadFront: ThreadFront,
   tabTarget: Target,
   actions: Actions,
   debuggerClient: DebuggerClient,
@@ -40,19 +46,31 @@ function setupEvents(dependencies: Depen
   actions = dependencies.actions;
   sourceQueue.initialize(actions);
 
   addThreadEventListeners(threadFront);
   tabTarget.on("workerListChanged", () => threadListChanged("worker"));
   debuggerClient.mainRoot.on("processListChanged", () =>
     threadListChanged("contentProcess")
   );
+
+  // If we are attaching to service workers we need to listen to worker changes
+  // everywhere in the browser.
+  if (features.windowlessServiceWorkers) {
+    const workersListener = new WorkersListener(debuggerClient.mainRoot);
+    workersListener.addListener(() => threadListChanged("worker"));
+  }
 }
 
 async function paused(threadFront: ThreadFront, packet: PausedPacket) {
+  // When reloading we might get pauses from threads before they have been
+  // added to the store. Ensure the pause won't be processed until we've
+  // finished adding the thread.
+  await actions.ensureHasThread(threadFront.actor);
+
   // If paused by an explicit interrupt, which are generated by the
   // slow script dialog and internal events such as setting
   // breakpoints, ignore the event.
   const { why } = packet;
   if (why.type === "interrupted" && !packet.why.onNext) {
     isInterrupted = true;
     return;
   }

--- a/devtools/client/debugger/src/client/firefox/targets.js
+++ b/devtools/client/debugger/src/client/firefox/targets.js
@@ -1,16 +1,17 @@
 /* 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/>. */
 
 // @flow
 
 import { addThreadEventListeners } from "./events";
-import { prefs } from "../../utils/prefs";
+import { prefs, features } from "../../utils/prefs";
+import { sameOrigin } from "../../utils/url";
 import type { DebuggerClient, Target } from "./types";
 import type { ThreadType } from "../../types";
 
 // $FlowIgnore
 const { defaultThreadOptions } = require("devtools/client/shared/thread-utils");
 
 type Args = {
   currentTarget: Target,
@@ -59,22 +60,35 @@ async function attachTargets(type, targe
     } catch (e) {
       // If any of the workers have terminated since the list command initiated
       // then we will get errors. Ignore these.
     }
   }
 }
 
 export async function updateWorkerTargets(type: ThreadType, args: Args) {
-  const { currentTarget } = args;
+  const { currentTarget, debuggerClient } = args;
   if (!currentTarget.isBrowsingContext || currentTarget.isContentProcess) {
     return;
   }
 
   const { workers } = await currentTarget.listWorkers();
+
+  if (features.windowlessServiceWorkers && currentTarget.url) {
+    const { service } = await debuggerClient.mainRoot.listAllWorkers();
+    for (const { active, id, url } of service) {
+      // Attach to any service workers that are same-origin with our target.
+      // For now, ignore service workers associated with cross-origin iframes.
+      if (active && sameOrigin(url, currentTarget.url)) {
+        const workerTarget = await debuggerClient.mainRoot.getWorker(id);
+        workers.push(workerTarget);
+      }
+    }
+  }
+
   await attachTargets(type, workers, args);
 }
 
 export async function updateProcessTargets(type: ThreadType, args: Args) {
   const { currentTarget, debuggerClient } = args;
   if (!prefs.fission || !currentTarget.chrome || currentTarget.isAddon) {
     return;
   }

--- a/devtools/client/debugger/src/client/firefox/types.js
+++ b/devtools/client/debugger/src/client/firefox/types.js
@@ -181,16 +181,17 @@ export type TabPayload = {
  * @static
  */
 export type Actions = {
   paused: Pause => void,
   resumed: ActorId => void,
   newQueuedSources: (QueuedSourceData[]) => void,
   fetchEventListeners: () => void,
   updateThreads: typeof actions.updateThreads,
+  ensureHasThread: typeof actions.ensureHasThread,
   setFramePositions: typeof actions.setFramePositions,
 };
 
 type ConsoleClient = {
   evaluateJS: (
     script: Script,
     func: Function,
     params?: { frameActor: ?FrameId }
@@ -251,16 +252,18 @@ export type DebuggerClient = {
   _activeRequests: {
     get: any => any,
     delete: any => void,
   },
   mainRoot: {
     traits: any,
     getFront: string => Promise<*>,
     listProcesses: () => Promise<{ processes: ProcessDescriptor }>,
+    listAllWorkers: () => Promise<*>,
+    getWorker: any => Promise<*>,
     on: (string, Function) => void,
   },
   connect: () => Promise<*>,
   request: (packet: Object) => Promise<*>,
   attachConsole: (actor: String, listeners: Array<*>) => Promise<*>,
   createObjectFront: (grip: Grip) => ObjectFront,
   release: (actor: String) => {},
   getFrontByID: (actor: String) => { release: () => Promise<*> },

--- a/devtools/client/debugger/src/utils/prefs.js
+++ b/devtools/client/debugger/src/utils/prefs.js
@@ -138,16 +138,17 @@ export const features = new PrefsHelper(
   xhrBreakpoints: ["Bool", "xhr-breakpoints"],
   originalBlackbox: ["Bool", "original-blackbox"],
   eventListenersBreakpoints: ["Bool", "event-listeners-breakpoints"],
   domMutationBreakpoints: ["Bool", "dom-mutation-breakpoints"],
   logPoints: ["Bool", "log-points"],
   showOverlay: ["Bool", "overlay"],
   inlinePreview: ["Bool", "inline-preview"],
   watchpoints: ["Bool", "watchpoints"],
+  windowlessServiceWorkers: ["Bool", "windowless-service-workers"],
 });
 
 export const asyncStore = asyncStoreHelper("debugger", {
   pendingBreakpoints: ["pending-breakpoints", {}],
   tabs: ["tabs", []],
   xhrBreakpoints: ["xhr-breakpoints", []],
   eventListenerBreakpoints: ["event-listener-breakpoints", undefined],
 });

--- a/devtools/client/debugger/src/utils/url.js
+++ b/devtools/client/debugger/src/utils/url.js
@@ -32,8 +32,12 @@ export const parse = memoize(function pa
     // If we're given simply a filename...
     if (url) {
       return { ...defaultUrl, path: url, pathname: url };
     }
 
     return defaultUrl;
   }
 });
+
+export function sameOrigin(firstUrl: string, secondUrl: string) {
+  return parse(firstUrl).origin == parse(secondUrl).origin;
+}

--- a/devtools/client/debugger/test/mochitest/browser.ini
+++ b/devtools/client/debugger/test/mochitest/browser.ini
@@ -154,16 +154,17 @@ skip-if = os == "win"
 [browser_dbg-tabs-without-urls.js]
 [browser_dbg-toggling-tools.js]
 [browser_dbg-react-app.js]
 skip-if = os == "win"
 [browser_dbg-wasm-sourcemaps.js]
 [browser_dbg-windowless-workers.js]
 [browser_dbg-windowless-workers-early-breakpoint.js]
 [browser_dbg-worker-exception.js]
+[browser_dbg-windowless-service-workers.js]
 [browser_dbg-worker-scopes.js]
 skip-if = (os == 'linux' && debug) || (os == 'linux' && asan) || ccov  #Bug 1456013, Bug 1559547
 [browser_dbg-event-handler.js]
 [browser_dbg-event-breakpoints.js]
 [browser_dbg-eval-throw.js]
 [browser_dbg-sourceURL-breakpoint.js]
 [browser_dbg-old-breakpoint.js]
 [browser_dbg-idb-run-to-completion.js]

--- a/devtools/client/debugger/test/mochitest/browser_dbg-bfcache.js
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-bfcache.js
@@ -1,12 +1,14 @@
 /* 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/>. */
 
+PromiseTestUtils.whitelistRejectionsGlobally(/Connection closed/);
+
 // Test that sources appear in the debugger when navigating using the BFCache.
 add_task(async function() {
   const dbg = await initDebugger("doc-bfcache1.html");
   await navigate(dbg, "doc-bfcache2.html", "doc-bfcache2.html");
   invokeInTab("goBack");
   await waitForSources(dbg, "doc-bfcache1.html");
   invokeInTab("goForward");
   await waitForSources(dbg, "doc-bfcache2.html");

new file mode 100644
--- /dev/null
+++ b/devtools/client/debugger/test/mochitest/browser_dbg-windowless-service-workers.js
@@ -0,0 +1,68 @@
+/* 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/>. */
+
+// Test that we can detect a new service worker and hit breakpoints that we've
+// set in it.
+add_task(async function() {
+  await pushPref("devtools.debugger.features.windowless-service-workers", true);
+  await pushPref("devtools.debugger.workers-visible", true);
+  await pushPref("dom.serviceWorkers.enabled", true);
+  await pushPref("dom.serviceWorkers.testing.enabled", true);
+
+  let dbg = await initDebugger("doc-service-workers.html");
+
+  invokeInTab("registerWorker");
+
+  await waitForSource(dbg, "service-worker.js");
+  const workerSource = findSource(dbg, "service-worker.js");
+
+  await addBreakpoint(dbg, "service-worker.js", 14);
+
+  invokeInTab("fetchFromWorker");
+
+  await waitForPaused(dbg);
+  assertPausedAtSourceAndLine(dbg, workerSource.id, 14);
+
+  await dbg.actions.removeAllBreakpoints(getContext(dbg));
+
+  await resume(dbg);
+
+  // Leave the worker registration in place for the next task.
+
+  // Set startup breakpoint for the next test.
+  //await addBreakpoint(dbg, "service-worker.js", 6);
+});
+
+async function checkWorkerThreads(dbg, count) {
+  await waitUntil(() => dbg.selectors.getThreads().length == count);
+  ok(true, `Have ${count} threads`);
+}
+
+// Test that service workers remain after reloading.
+add_task(async function() {
+  const toolbox = await openNewTabAndToolbox(EXAMPLE_URL + "doc-service-workers.html", "jsdebugger");
+  const dbg = createDebuggerContext(toolbox);
+
+  await checkWorkerThreads(dbg, 1);
+
+  await reload(dbg);
+
+  await waitForSource(dbg, "service-worker.js");
+  const workerSource = findSource(dbg, "service-worker.js");
+
+  await addBreakpoint(dbg, "service-worker.js", 14);
+
+  invokeInTab("fetchFromWorker");
+
+  await waitForPaused(dbg);
+  assertPausedAtSourceAndLine(dbg, workerSource.id, 14);
+  await checkWorkerThreads(dbg, 1);
+
+  await resume(dbg);
+
+  invokeInTab("unregisterWorker");
+
+  await dbg.actions.removeAllBreakpoints(getContext(dbg));
+  await checkWorkerThreads(dbg, 0);
+});

new file mode 100644
--- /dev/null
+++ b/devtools/client/debugger/test/mochitest/examples/doc-service-workers.html
@@ -0,0 +1,32 @@
+<script>
+async function registerWorker() {
+  const sw = navigator.serviceWorker;
+  const swr = await sw.register("service-worker.js", { scope: "" });
+  dump(`Registered, scope is: ${swr.scope}\n`);
+
+  await new Promise(resolve => {
+    const worker = swr.installing || swr.waiting || swr.active;
+    if (worker.state === 'activated') {
+      return resolve();
+    }
+
+    worker.addEventListener('statechange', () => {
+      if (worker.state === 'activated') {
+        return resolve();
+      }
+    });
+  });
+}
+
+async function unregisterWorker() {
+  const sw = navigator.serviceWorker;
+  const swr = await sw.register("service-worker.js", { scope: "" });
+  return swr.unregister();
+}
+
+async function fetchFromWorker() {
+  const response = await fetch("whatever");
+  const text = await response.text();
+  console.log(`Response ${text}`);
+}
+</script>

new file mode 100644
--- /dev/null
+++ b/devtools/client/debugger/test/mochitest/examples/service-worker.js
@@ -0,0 +1,20 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+dump("Starting\n");
+
+self.addEventListener("activate", event => {
+  dump("Activate\n");
+  event.waitUntil(self.clients.claim());
+});
+
+self.addEventListener("fetch", event => {
+  const url = event.request.url;
+  dump(`Fetch: ${url}\n`);
+  if (url.includes("whatever")) {
+    const response = new Response("Service worker response", { statusText: "OK" });
+    event.respondWith(response);
+  }
+});

--- a/devtools/client/preferences/debugger.js
+++ b/devtools/client/preferences/debugger.js
@@ -80,8 +80,9 @@ pref("devtools.debugger.features.autocom
 pref("devtools.debugger.features.map-expression-bindings", true);
 pref("devtools.debugger.features.xhr-breakpoints", true);
 pref("devtools.debugger.features.original-blackbox", true);
 pref("devtools.debugger.features.event-listeners-breakpoints", true);
 pref("devtools.debugger.features.dom-mutation-breakpoints", true);
 pref("devtools.debugger.features.log-points", true);
 pref("devtools.debugger.features.overlay", true);
 pref("devtools.debugger.features.inline-preview", true);
+pref("devtools.debugger.features.windowless-service-workers", false);

--- a/devtools/client/responsive/browser/tunnel.js
+++ b/devtools/client/responsive/browser/tunnel.js
@@ -133,17 +133,16 @@ function tunnelToInnerBrowser(outer, inn
       }
       if (!inner.isRemoteBrowser) {
         throw new Error("The inner browser must be remote.");
       }
 
       // Various browser methods access the `frameLoader` property, including:
       //   * `saveBrowser` from contentAreaUtils.js
       //   * `docShellIsActive` from browser.js
-      //   * `hasContentOpener` from browser.js
       //   * `preserveLayers` from browser.js
       //   * `receiveMessage` from SessionStore.jsm
       // In general, these methods are interested in the `frameLoader` for the content,
       // so we redirect them to the inner browser's `frameLoader`.
       outer[FRAME_LOADER] = outer.frameLoader;
       Object.defineProperty(outer, "frameLoader", {
         get() {
           const stack = getStack();

--- a/devtools/client/webconsole/test/browser/browser.ini
+++ b/devtools/client/webconsole/test/browser/browser.ini
@@ -387,17 +387,16 @@ skip-if = fission
 [browser_webconsole_input_focus.js]
 [browser_webconsole_insecure_passwords_about_blank_web_console_warning.js]
 [browser_webconsole_insecure_passwords_web_console_warning.js]
 [browser_webconsole_inspect_cross_domain_object.js]
 skip-if = fission
 [browser_webconsole_keyboard_accessibility.js]
 [browser_webconsole_location_debugger_link.js]
 [browser_webconsole_location_logpoint_debugger_link.js]
-skip-if = (os == 'linux' && bits == 64) || (os == 'win') # Bug 1583706
 [browser_webconsole_location_styleeditor_link.js]
 [browser_webconsole_logErrorInPage.js]
 [browser_webconsole_loglimit.js]
 [browser_webconsole_logWarningInPage.js]
 [browser_webconsole_longstring_getter.js]
 [browser_webconsole_longstring.js]
 [browser_webconsole_message_categories.js]
 skip-if = fission

--- a/devtools/server/actors/replay/control.js
+++ b/devtools/server/actors/replay/control.js
@@ -334,23 +334,25 @@ function closestChild(point) {
 
 // The singleton ReplayDebugger, or undefined if it doesn't exist.
 let gDebugger;
 
 ////////////////////////////////////////////////////////////////////////////////
 // Asynchronous Manifests
 ////////////////////////////////////////////////////////////////////////////////
 
-// Asynchronous manifest worklists.
-const gAsyncManifests = new Set();
-const gAsyncManifestsLowPriority = new Set();
+// Priority levels for asynchronous manifests.
+const Priority = {
+  HIGH: 0,
+  MEDIUM: 1,
+  LOW: 2,
+};
 
-function asyncManifestWorklist(lowPriority) {
-  return lowPriority ? gAsyncManifestsLowPriority : gAsyncManifests;
-}
+// Asynchronous manifest worklists.
+const gAsyncManifests = [new Set(), new Set(), new Set()];
 
 // Send a manifest asynchronously, returning a promise that resolves when the
 // manifest has been finished. Async manifests have the following properties:
 //
 // shouldSkip: Callback invoked before sending the manifest. Returns true if the
 //   manifest should not be sent, and the promise resolved immediately.
 //
 // contents: Callback invoked with the executing child when it is being sent.
@@ -364,36 +366,36 @@ function asyncManifestWorklist(lowPriori
 //
 // snapshot: Optional point at which the associated child should take a snapshot
 //   while heading to the point.
 //
 // scanCheckpoint: If the manifest relies on scan data, the saved checkpoint
 //   whose range the child must have scanned. Such manifests do not have side
 //   effects in the child, and can be sent to the active child.
 //
-// lowPriority: True if this manifest should be processed only after all other
-//   manifests have been processed.
+// priority: Optional priority for this manifest. Default is HIGH.
 //
 // destination: An optional destination where the child will end up.
 //
 // expectedDuration: Optional estimate of the time needed to run the manifest.
 //
 // mightRewind: Flag that must be set if the child might restore a snapshot
 //   while processing the manifest.
 function sendAsyncManifest(manifest) {
   pokeChildrenSoon();
   return new Promise(resolve => {
     manifest.resolve = resolve;
-    asyncManifestWorklist(manifest.lowPriority).add(manifest);
+    const priority = manifest.priority || Priority.HIGH;
+    gAsyncManifests[priority].add(manifest);
   });
 }
 
 // Pick the best async manifest for a child to process.
-function pickAsyncManifest(child, lowPriority) {
-  const worklist = asyncManifestWorklist(lowPriority);
+function pickAsyncManifest(child, priority) {
+  const worklist = gAsyncManifests[priority];
 
   let best = null,
     bestTime = Infinity;
   for (const manifest of worklist) {
     // Prune any manifests that can be skipped.
     if (manifest.shouldSkip()) {
       manifest.resolve();
       worklist.delete(manifest);
@@ -442,22 +444,24 @@ function processAsyncManifest(child) {
   if (manifest && child == gActiveChild) {
     // After a child becomes the active child, it gives up on any in progress
     // async manifest it was processing.
     sendAsyncManifest(manifest);
     manifest = null;
   }
 
   if (!manifest) {
-    manifest = pickAsyncManifest(child, /* lowPriority */ false);
+    for (const priority of Object.values(Priority)) {
+      manifest = pickAsyncManifest(child, priority);
+      if (manifest) {
+        break;
+      }
+    }
     if (!manifest) {
-      manifest = pickAsyncManifest(child, /* lowPriority */ true);
-      if (!manifest) {
-        return false;
-      }
+      return false;
     }
   }
 
   child.asyncManifest = manifest;
 
   if (
     manifest.point &&
     maybeReachPoint(child, manifest.point, manifest.snapshot)
@@ -1034,17 +1038,17 @@ async function queuePauseData({
       if (!data.restoredSnapshot) {
         addPauseData(point, data, trackCached);
         child.divergedFromRecording = true;
       }
     },
     point,
     snapshot,
     expectedDuration: 250,
-    lowPriority: true,
+    priority: Priority.LOW,
     mightRewind: true,
   });
 }
 
 function addPauseData(point, data, trackCached) {
   if (data.paintData) {
     // Atomize paint data strings to ensure that we don't store redundant
     // strings for execution points with the same paint data.
@@ -1571,17 +1575,17 @@ async function evaluateLogpoint({
         if (!fast) {
           child.divergedFromRecording = true;
         }
       }
     },
     point,
     snapshot,
     expectedDuration: 250,
-    lowPriority: true,
+    priority: Priority.MEDIUM,
     mightRewind: true,
   });
 }
 
 // Asynchronously invoke a logpoint's callback with all results from hitting
 // the logpoint in the range of the recording covered by checkpoint.
 async function findLogpointHits(
   checkpoint,

--- a/dom/animation/test/chrome/test_running_on_compositor.html
+++ b/dom/animation/test/chrome/test_running_on_compositor.html
@@ -1112,64 +1112,107 @@ promise_test(async t => {
   properties.forEach(property => {
     assert_true(property.runningOnCompositor,
                 property.property + ' is running on the compositor');
   });
 }, 'Multiple transform-like properties animation runs on the compositor');
 
 promise_test(async t => {
   const div = addDiv(t);
+  const animation = div.animate({ offsetPath: ['none', 'none'] },
+                                100 * MS_PER_SEC);
+
+  await waitForAnimationReadyToRestyle(animation);
+  await waitForPaints();
+
+  assert_animation_is_running_on_compositor(animation,
+    'offset-path animation should be running on the compositor even if ' +
+    'it is always none');
+}, 'offset-path none animation runs on the compositor');
+
+promise_test(async t => {
+  const div = addDiv(t);
   const animation = div.animate({ offsetPath: ['path("M0 0l100 100")',
                                                'path("M0 0l200 200")'] },
                                 100 * MS_PER_SEC);
 
   await waitForAnimationReadyToRestyle(animation);
   await waitForPaints();
 
   assert_animation_is_running_on_compositor(animation,
     'offset-path animation should be running on the compositor');
 }, 'offset-path animation runs on the compositor');
 
-// FIXME:  Bug 1592787: We should stop sending offset-* properties to the
-// compositor and skip restyling entirely if offset-path is none and we don't
-// have any animation of it.
 promise_test(async t => {
   const div = addDiv(t);
   const animation = div.animate({ offsetDistance: ['0%', '100%'] },
                                 100 * MS_PER_SEC);
 
   await waitForAnimationReadyToRestyle(animation);
   await waitForPaints();
 
+  assert_animation_is_not_running_on_compositor(animation,
+    'offset-distance animation is not running on the compositor because ' +
+    'offset-path is none');
+
+  const newAnim = div.animate({ offsetPath: ['None', 'None'] },
+                              100 * MS_PER_SEC);
+  await waitForAnimationReadyToRestyle(newAnim);
+  await waitForPaints();
+
   assert_animation_is_running_on_compositor(animation,
     'offset-distance animation should be running on the compositor');
+  assert_animation_is_running_on_compositor(newAnim,
+    'new added offset-path animation should be running on the compositor');
 }, 'offset-distance animation runs on the compositor');
 
 promise_test(async t => {
   const div = addDiv(t);
   const animation = div.animate({ offsetRotate: ['0deg', '45deg'] },
                                 100 * MS_PER_SEC);
 
   await waitForAnimationReadyToRestyle(animation);
   await waitForPaints();
 
+  assert_animation_is_not_running_on_compositor(animation,
+    'offset-rotate animation is not running on the compositor because ' +
+    'offset-path is none');
+
+  const newAnim = div.animate({ offsetPath: ['None', 'None'] },
+                              100 * MS_PER_SEC);
+  await waitForAnimationReadyToRestyle(newAnim);
+  await waitForPaints();
+
   assert_animation_is_running_on_compositor(animation,
     'offset-rotate animation should be running on the compositor');
+  assert_animation_is_running_on_compositor(newAnim,
+    'new added offset-path animation should be running on the compositor');
 }, 'offset-rotate animation runs on the compositor');
 
 promise_test(async t => {
   const div = addDiv(t);
   const animation = div.animate({ offsetAnchor: ['0% 0%', '100% 100%'] },
                                 100 * MS_PER_SEC);
 
   await waitForAnimationReadyToRestyle(animation);
   await waitForPaints();
 
+  assert_animation_is_not_running_on_compositor(animation,
+    'offset-anchor animation is not running on the compositor because ' +
+    'offset-path is none');
+
+  const newAnim = div.animate({ offsetPath: ['None', 'None'] },
+                              100 * MS_PER_SEC);
+  await waitForAnimationReadyToRestyle(newAnim);
+  await waitForPaints();
+
   assert_animation_is_running_on_compositor(animation,
     'offset-anchor animation should be running on the compositor');
+  assert_animation_is_running_on_compositor(newAnim,
+    'new added offset-path animation should be running on the compositor');
 }, 'offset-anchor animation runs on the compositor');
 
 promise_test(async t => {
   const div = addDiv(t);
   const animation = div.animate({ translate: ['0px', '100px'],
                                   rotate: ['0deg', '45deg'],
                                   transform: ['translate(0px)',
                                               'translate(100px)'],

--- a/dom/base/BindContext.h
+++ b/dom/base/BindContext.h
@@ -4,19 +4,16 @@
  * 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/. */
 
 /* State that is passed down to BindToTree. */
 
 #ifndef mozilla_dom_BindContext_h__
 #define mozilla_dom_BindContext_h__
 
-#ifdef MOZ_XBL
-#  include "nsXBLBinding.h"
-#endif
 #include "mozilla/Attributes.h"
 #include "mozilla/AutoRestore.h"
 #include "mozilla/dom/Document.h"
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/ShadowRoot.h"
 
 namespace mozilla {
 namespace dom {
@@ -94,29 +91,16 @@ struct MOZ_STACK_CLASS BindContext final
         mInUncomposedDoc(aParentElement.IsInUncomposedDoc()),
         mSubtreeRootChanges(true),
         mCollectingDisplayedNodeDataDuringLoad(
             ShouldCollectDisplayedNodeDataDuringLoad(mInComposedDoc, mDoc,
                                                      aParentElement)) {
     MOZ_ASSERT(mInComposedDoc, "Binding NAC in a disconnected subtree?");
   }
 
-#ifdef MOZ_XBL
-  // This is meant to be used to bind XBL anonymous content.
-  BindContext(nsXBLBinding& aBinding, Element& aParentElement)
-      : mDoc(*aParentElement.OwnerDoc()),
-        mBindingParent(aBinding.GetBoundElement()),
-        mInComposedDoc(aParentElement.IsInComposedDoc()),
-        mInUncomposedDoc(aParentElement.IsInUncomposedDoc()),
-        mSubtreeRootChanges(true),
-        mCollectingDisplayedNodeDataDuringLoad(
-            ShouldCollectDisplayedNodeDataDuringLoad(mInComposedDoc, mDoc,
-                                                     aParentElement)) {}
-#endif
-
   bool CollectingDisplayedNodeDataDuringLoad() const {
     return mCollectingDisplayedNodeDataDuringLoad;
   }
 
  private:
   static bool IsLikelyUndisplayed(const nsINode& aParent) {
     return aParent.IsAnyOfHTMLElements(nsGkAtoms::style, nsGkAtoms::script);
   }

--- a/dom/base/CharacterData.cpp
+++ b/dom/base/CharacterData.cpp
@@ -24,19 +24,16 @@
 #include "nsReadableUtils.h"
 #include "mozilla/InternalMutationEvent.h"
 #include "nsIURI.h"
 #include "nsCOMPtr.h"
 #include "nsDOMString.h"
 #include "nsChangeHint.h"
 #include "nsCOMArray.h"
 #include "mozilla/dom/DirectionalityUtils.h"
-#ifdef MOZ_XBL
-#  include "nsBindingManager.h"
-#endif
 #include "nsCCUncollectableMarker.h"
 #include "mozAutoDocUpdate.h"
 #include "nsTextNode.h"
 #include "nsBidiUtils.h"
 #include "PLDHashTable.h"
 #include "mozilla/Sprintf.h"
 #include "nsWindowSizes.h"
 #include "nsWrapperCacheInlines.h"
@@ -510,20 +507,16 @@ nsresult CharacterData::BindToTree(BindC
 }
 
 void CharacterData::UnbindFromTree(bool aNullParent) {
   // Unset frame flags; if we need them again later, they'll get set again.
   UnsetFlags(NS_CREATE_FRAME_IF_NON_WHITESPACE | NS_REFRAME_IF_WHITESPACE);
 
   HandleShadowDOMRelatedRemovalSteps(aNullParent);
 
-#ifdef MOZ_XBL
-  Document* document = GetComposedDoc();
-#endif
-
   if (aNullParent) {
     if (IsRootOfNativeAnonymousSubtree()) {
       MutationObservers::NotifyNativeAnonymousChildListChange(this, true);
     }
     if (GetParent()) {
       NS_RELEASE(mParent);
     } else {
       mParent = nullptr;
@@ -535,29 +528,16 @@ void CharacterData::UnbindFromTree(bool 
 
   if (aNullParent || !mParent->IsInShadowTree()) {
     UnsetFlags(NODE_IS_IN_SHADOW_TREE);
 
     // Begin keeping track of our subtree root.
     SetSubtreeRootPointer(aNullParent ? this : mParent->SubtreeRoot());
   }
 
-#ifdef MOZ_XBL
-  if (document && !GetContainingShadow()) {
-    // Notify XBL- & nsIAnonymousContentCreator-generated
-    // anonymous content that the document is changing.
-    // Unlike XBL, bindings for web components shadow DOM
-    // do not get uninstalled.
-    if (HasFlag(NODE_MAY_BE_IN_BINDING_MNGR)) {
-      nsContentUtils::AddScriptRunner(new RemoveFromBindingManagerRunnable(
-          document->BindingManager(), this, document));
-    }
-  }
-#endif
-
   nsExtendedContentSlots* slots = GetExistingExtendedContentSlots();
   if (slots) {
     slots->mBindingParent = nullptr;
     if (aNullParent || !mParent->IsInShadowTree()) {
       slots->mContainingShadow = nullptr;
     }
   }
 

--- a/dom/base/CharacterData.h
+++ b/dom/base/CharacterData.h
@@ -164,20 +164,16 @@ class CharacterData : public nsIContent 
   void SaveSubtreeState() final {}
 
 #ifdef DEBUG
   void List(FILE* out, int32_t aIndent) const override {}
 
   void DumpContent(FILE* out, int32_t aIndent, bool aDumpAll) const override {}
 #endif
 
-#ifdef MOZ_XBL
-  nsXBLBinding* DoGetXBLBinding() const final { return nullptr; }
-#endif
-
   bool IsNodeOfType(uint32_t aFlags) const override { return false; }
 
   bool IsLink(nsIURI** aURI) const final {
     *aURI = nullptr;
     return false;
   }
 
   nsresult Clone(dom::NodeInfo* aNodeInfo, nsINode** aResult) const override {

--- a/dom/base/ChildIterator.cpp
+++ b/dom/base/ChildIterator.cpp
@@ -3,19 +3,16 @@
 /* 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/. */
 
 #include "ChildIterator.h"
 #include "nsContentUtils.h"
 #include "mozilla/dom/Document.h"
 #include "mozilla/dom/HTMLSlotElement.h"
-#ifdef MOZ_XBL
-#  include "mozilla/dom/XBLChildrenElement.h"
-#endif
 #include "mozilla/dom/ShadowRoot.h"
 #include "nsIAnonymousContentCreator.h"
 #include "nsIFrame.h"
 #include "nsCSSAnonBoxes.h"
 
 namespace mozilla {
 namespace dom {
 
@@ -43,27 +40,17 @@ nsIContent* ExplicitChildIterator::GetNe
                    ? assignedNodes[mIndexInInserted++]->AsContent()
                    : nullptr;
       if (!mChild) {
         mIndexInInserted = 0;
       }
       return mChild;
     }
 
-#ifdef MOZ_XBL
-    MOZ_ASSERT(mChild->IsActiveChildrenElement());
-    auto* childrenElement = static_cast<XBLChildrenElement*>(mChild);
-    if (mIndexInInserted < childrenElement->InsertedChildrenLength()) {
-      return childrenElement->InsertedChild(mIndexInInserted++);
-    }
-    mIndexInInserted = 0;
-    mChild = mChild->GetNextSibling();
-#else
     MOZ_ASSERT_UNREACHABLE("This needs to be revisited");
-#endif
   } else if (mDefaultChild) {
     // If we're already in default content, check if there are more nodes there
     MOZ_ASSERT(mChild);
     MOZ_ASSERT(mChild->IsActiveChildrenElement());
 
     mDefaultChild = mDefaultChild->GetNextSibling();
     if (mDefaultChild) {
       return mDefaultChild;
@@ -89,40 +76,17 @@ nsIContent* ExplicitChildIterator::GetNe
   } else if (mChild) {  // in the middle of the child list
     mChild = mChild->GetNextSibling();
   }
 
   // Iterate until we find a non-insertion point, or an insertion point with
   // content.
   while (mChild) {
     if (mChild->IsActiveChildrenElement()) {
-#ifdef MOZ_XBL
-      // If the current child being iterated is a content insertion point
-      // then the iterator needs to return the nodes distributed into
-      // the content insertion point.
-      auto* childrenElement = static_cast<XBLChildrenElement*>(mChild);
-      if (childrenElement->HasInsertedChildren()) {
-        // Iterate through elements projected on insertion point.
-        mIndexInInserted = 1;
-        return childrenElement->InsertedChild(0);
-      }
-
-      // Insertion points inside fallback/default content
-      // are considered inactive and do not get assigned nodes.
-      mDefaultChild = mChild->GetFirstChild();
-      if (mDefaultChild) {
-        return mDefaultChild;
-      }
-
-      // If we have an insertion point with no assigned nodes and
-      // no default content, move on to the next node.
-      mChild = mChild->GetNextSibling();
-#else
       MOZ_ASSERT_UNREACHABLE("This needs to be revisited");
-#endif
     } else {
       // mChild is not an insertion point, thus it is the next node to
       // return from this iterator.
       break;
     }
   }
 
   return mChild;
@@ -138,27 +102,16 @@ void FlattenedChildIterator::Init(bool a
   // FlattenedChildIterators with Element.
   if (mParent->IsElement()) {
     if (ShadowRoot* shadow = mParent->AsElement()->GetShadowRoot()) {
       mParent = shadow;
       mXBLInvolved = Some(true);
       return;
     }
   }
-
-#ifdef MOZ_XBL
-  nsXBLBinding* binding =
-      mParent->OwnerDoc()->BindingManager()->GetBindingWithContent(mParent);
-
-  if (binding) {
-    MOZ_ASSERT(binding->GetAnonymousContent());
-    mParent = binding->GetAnonymousContent();
-    mXBLInvolved = Some(true);
-  }
-#endif
 }
 
 bool FlattenedChildIterator::ComputeWhetherXBLIsInvolved() const {
   MOZ_ASSERT(mXBLInvolved.isNothing());
   // We set mXBLInvolved to true if either the node we're iterating has a
   // binding with content attached to it (in which case it is handled in Init),
   // the node is generated XBL content and has an <xbl:children> child, or the
   // node is a <slot> element.
@@ -206,23 +159,17 @@ nsIContent* ExplicitChildIterator::Get()
 
   // When mParentAsSlot is set, mChild is always set to the current child. It
   // does not matter whether mChild is an assigned node or a fallback content.
   if (mParentAsSlot) {
     return mChild;
   }
 
   if (mIndexInInserted) {
-#ifdef MOZ_XBL
-    MOZ_ASSERT(mChild->IsActiveChildrenElement());
-    auto* childrenElement = static_cast<XBLChildrenElement*>(mChild);
-    return childrenElement->InsertedChild(mIndexInInserted - 1);
-#else
     MOZ_ASSERT_UNREACHABLE("This needs to be revisited");
-#endif
   }
 
   return mDefaultChild ? mDefaultChild : mChild;
 }
 
 nsIContent* ExplicitChildIterator::GetPreviousChild() {
   // If we're already in the inserted-children array, look there first
   if (mIndexInInserted) {
@@ -235,28 +182,17 @@ nsIContent* ExplicitChildIterator::GetPr
                    : nullptr;
 
       if (!mChild) {
         mIsFirst = true;
       }
       return mChild;
     }
 
-#ifdef MOZ_XBL
-    // NB: mIndexInInserted points one past the last returned child so we need
-    // to look *two* indices back in order to return the previous child.
-    MOZ_ASSERT(mChild->IsActiveChildrenElement());
-    auto* childrenElement = static_cast<XBLChildrenElement*>(mChild);
-    if (--mIndexInInserted) {
-      return childrenElement->InsertedChild(mIndexInInserted - 1);
-    }
-    mChild = mChild->GetPreviousSibling();
-#else
     MOZ_ASSERT_UNREACHABLE("This needs to be revisited");
-#endif
   } else if (mDefaultChild) {
     // If we're already in default content, check if there are more nodes there
     mDefaultChild = mDefaultChild->GetPreviousSibling();
     if (mDefaultChild) {
       return mDefaultChild;
     }
 
     mChild = mChild->GetPreviousSibling();
@@ -279,35 +215,17 @@ nsIContent* ExplicitChildIterator::GetPr
 
     mChild = mParent->GetLastChild();
   }
 
   // Iterate until we find a non-insertion point, or an insertion point with
   // content.
   while (mChild) {
     if (mChild->IsActiveChildrenElement()) {
-#ifdef MOZ_XBL
-      // If the current child being iterated is a content insertion point
-      // then the iterator needs to return the nodes distributed into
-      // the content insertion point.
-      auto* childrenElement = static_cast<XBLChildrenElement*>(mChild);
-      if (childrenElement->HasInsertedChildren()) {
-        mIndexInInserted = childrenElement->InsertedChildrenLength();
-        return childrenElement->InsertedChild(mIndexInInserted - 1);
-      }
-
-      mDefaultChild = mChild->GetLastChild();
-      if (mDefaultChild) {
-        return mDefaultChild;
-      }
-
-      mChild = mChild->GetPreviousSibling();
-#else
       MOZ_ASSERT_UNREACHABLE("This needs to be revisited");
-#endif
     } else {
       // mChild is not an insertion point, thus it is the next node to
       // return from this iterator.
       break;
     }
   }
 
   if (!mChild) {

--- a/dom/base/Document.cpp
+++ b/dom/base/Document.cpp
@@ -174,19 +174,16 @@
 #include "nsICookiePermission.h"
 #include "nsICookieService.h"
 
 #include "nsBidiUtils.h"
 
 #include "nsContentCreatorFunctions.h"
 
 #include "nsIScriptContext.h"
-#ifdef MOZ_XBL
-#  include "nsBindingManager.h"
-#endif
 #include "nsHTMLDocument.h"
 #include "nsIRequest.h"
 #include "mozilla/dom/BlobURLProtocolHandler.h"
 
 #include "nsCharsetSource.h"
 #include "nsIParser.h"
 #include "nsIContentSink.h"
 
@@ -1943,25 +1940,16 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_
   } else {
     NS_IMPL_CYCLE_COLLECTION_DESCRIBE(Document, tmp->mRefCnt.get())
   }
 
   if (!nsINode::Traverse(tmp, cb)) {
     return NS_SUCCESS_INTERRUPTED_TRAVERSE;
   }
 
-#ifdef MOZ_XBL
-  if (tmp->mMaybeEndOutermostXBLUpdateRunner) {
-    // The cached runnable keeps a reference to the document object..
-    NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(
-        cb, "mMaybeEndOutermostXBLUpdateRunner.mObj");
-    cb.NoteXPCOMChild(ToSupports(tmp));
-  }
-#endif
-
   tmp->mExternalResourceMap.Traverse(&cb);
 
   // Traverse all Document pointer members.
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mSecurityInfo)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDisplayDocument)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mFontFaceSet)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mReadyForIdle)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDocumentL10n)
@@ -2080,19 +2068,16 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(Do
     tmp->DisconnectChild(child);
     child->UnbindFromTree();
   }
 
   tmp->UnlinkOriginalDocumentIfStatic();
 
   tmp->mCachedRootElement = nullptr;  // Avoid a dangling pointer
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mDisplayDocument)
-#ifdef MOZ_XBL
-  NS_IMPL_CYCLE_COLLECTION_UNLINK(mMaybeEndOutermostXBLUpdateRunner)
-#endif
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mDOMImplementation)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mImageMaps)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mCachedEncoder)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mDocumentTimeline)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mPendingAnimationTracker)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mTemplateContentsOwner)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mChildrenCollection)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mImages);
@@ -5908,32 +5893,16 @@ void Document::TryChannelCharset(nsIChan
 static inline void AssertNoStaleServoDataIn(nsINode& aSubtreeRoot) {
 #ifdef DEBUG
   for (nsINode* node : ShadowIncludingTreeIterator(aSubtreeRoot)) {
     const Element* element = Element::FromNode(node);
     if (!element) {
       continue;
     }
     MOZ_ASSERT(!element->HasServoData());
-#  ifdef MOZ_XBL
-    if (nsXBLBinding* binding = element->GetXBLBinding()) {
-      if (nsXBLBinding* bindingWithContent = binding->GetBindingWithContent()) {
-        nsIContent* content = bindingWithContent->GetAnonymousContent();
-        // Need to do this instead of just AssertNoStaleServoDataIn(*content),
-        // because the parent of the children of the <content> element isn't the
-        // <content> element, but the bound element, and that confuses
-        // GetNextNode a lot.
-        MOZ_ASSERT(!content->AsElement()->HasServoData());
-        for (nsINode* child = content->GetFirstChild(); child;
-             child = child->GetNextSibling()) {
-          AssertNoStaleServoDataIn(*child);
-        }
-      }
-    }
-#  endif
   }
 #endif
 }
 
 already_AddRefed<PresShell> Document::CreatePresShell(
     nsPresContext* aContext, nsViewManager* aViewManager) {
   MOZ_ASSERT(!mPresShell, "We have a presshell already!");
 
@@ -6919,76 +6888,43 @@ bool Document::RemoveObserver(nsIDocumen
   if (!mInDestructor) {
     RemoveMutationObserver(aObserver);
     return mObservers.RemoveElement(aObserver);
   }
 
   return mObservers.Contains(aObserver);
 }
 
-#ifdef MOZ_XBL
-void Document::MaybeEndOutermostXBLUpdate() {
-  // Only call BindingManager()->EndOutermostUpdate() when
-  // we're not in an update and it is safe to run scripts.
-  if (mUpdateNestLevel == 0 && mInXBLUpdate) {
-    if (nsContentUtils::IsSafeToRunScript()) {
-      mInXBLUpdate = false;
-      BindingManager()->EndOutermostUpdate();
-    } else if (!mInDestructor) {
-      if (!mMaybeEndOutermostXBLUpdateRunner) {
-        mMaybeEndOutermostXBLUpdateRunner =
-            NewRunnableMethod("Document::MaybeEndOutermostXBLUpdate", this,
-                              &Document::MaybeEndOutermostXBLUpdate);
-      }
-      nsContentUtils::AddScriptRunner(mMaybeEndOutermostXBLUpdateRunner);
-    }
-  }
-}
-#endif
-
 void Document::BeginUpdate() {
   // If the document is going away, then it's probably okay to do things to it
   // in the wrong DocGroup. We're unlikely to run JS or do anything else
   // observable at this point. We reach this point when cycle collecting a
   // <link> element and the unlink code removes a style sheet.
   //
   // TODO(emilio): Style updates are gone, can this happen now?
   if (mDocGroup && !mIsGoingAway && !mInUnlinkOrDeletion &&
       !mIgnoreDocGroupMismatches) {
     mDocGroup->ValidateAccess();
   }
 
-#ifdef MOZ_XBL
-  if (mUpdateNestLevel == 0 && !mInXBLUpdate) {
-    mInXBLUpdate = true;
-    BindingManager()->BeginOutermostUpdate();
-  }
-#endif
-
   ++mUpdateNestLevel;
   nsContentUtils::AddScriptBlocker();
   NS_DOCUMENT_NOTIFY_OBSERVERS(BeginUpdate, (this));
 }
 
 void Document::EndUpdate() {
   const bool reset = !mPendingMaybeEditingStateChanged;
   mPendingMaybeEditingStateChanged = true;
 
   NS_DOCUMENT_NOTIFY_OBSERVERS(EndUpdate, (this));
 
   nsContentUtils::RemoveScriptBlocker();
 
   --mUpdateNestLevel;
 
-#ifdef MOZ_XBL
-  // This set of updates may have created XBL bindings.  Let the
-  // binding manager know we're done.
-  MaybeEndOutermostXBLUpdate();
-#endif
-
   MaybeInitializeFinalizeFrameLoaders();
   if (mXULBroadcastManager) {
     mXULBroadcastManager->MaybeBroadcast();
   }
 
   if (reset) {
     mPendingMaybeEditingStateChanged = false;
   }
@@ -7869,88 +7805,29 @@ already_AddRefed<nsINode> Document::Impo
 Element* Document::GetBindingParent(nsINode& aNode) {
   nsCOMPtr<nsIContent> content(do_QueryInterface(&aNode));
   if (!content) return nullptr;
 
   nsIContent* bindingParent = content->GetBindingParent();
   return bindingParent ? bindingParent->AsElement() : nullptr;
 }
 
-#ifdef MOZ_XBL
-static Element* GetElementByAttribute(Element* aElement, nsAtom* aAttrName,
-                                      const nsAString& aAttrValue,
-                                      bool aUniversalMatch) {
-  if (aUniversalMatch ? aElement->HasAttr(kNameSpaceID_None, aAttrName)
-                      : aElement->AttrValueIs(kNameSpaceID_None, aAttrName,
-                                              aAttrValue, eCaseMatters)) {
-    return aElement;
-  }
-
-  for (nsIContent* child = aElement->GetFirstChild(); child;
-       child = child->GetNextSibling()) {
-    if (!child->IsElement()) {
-      continue;
-    }
-
-    Element* matchedElement = GetElementByAttribute(
-        child->AsElement(), aAttrName, aAttrValue, aUniversalMatch);
-    if (matchedElement) return matchedElement;
-  }
-
-  return nullptr;
-}
-#endif
-
 Element* Document::GetAnonymousElementByAttribute(
     nsIContent* aElement, nsAtom* aAttrName,
     const nsAString& aAttrValue) const {
-#ifdef MOZ_XBL
-  nsINodeList* nodeList = BindingManager()->GetAnonymousNodesFor(aElement);
-  if (!nodeList) return nullptr;
-
-  uint32_t length = nodeList->Length();
-
-  bool universalMatch = aAttrValue.EqualsLiteral("*");
-
-  for (uint32_t i = 0; i < length; ++i) {
-    Element* current = Element::FromNode(nodeList->Item(i));
-    if (!current) {
-      continue;
-    }
-
-    Element* matchedElm =
-        GetElementByAttribute(current, aAttrName, aAttrValue, universalMatch);
-    if (matchedElm) return matchedElm;
-  }
-
   return nullptr;
-#else
-  return nullptr;
-#endif
 }
 
 Element* Document::GetAnonymousElementByAttribute(Element& aElement,
                                                   const nsAString& aAttrName,
                                                   const nsAString& aAttrValue) {
-#ifdef MOZ_XBL
-  RefPtr<nsAtom> attribute = NS_Atomize(aAttrName);
-
-  return GetAnonymousElementByAttribute(&aElement, attribute, aAttrValue);
-#else
   return nullptr;
-#endif
-}
-
-nsINodeList* Document::GetAnonymousNodes(Element& aElement) {
-#ifdef MOZ_XBL
-  return BindingManager()->GetAnonymousNodesFor(&aElement);
-#else
-  return nullptr;
-#endif
-}
+}
+
+nsINodeList* Document::GetAnonymousNodes(Element& aElement) { return nullptr; }
 
 already_AddRefed<nsRange> Document::CreateRange(ErrorResult& rv) {
   RefPtr<nsRange> range = new nsRange(this);
   nsresult res = range->CollapseTo(this, 0);
   if (NS_FAILED(res)) {
     rv.Throw(res);
     return nullptr;
   }
@@ -9297,26 +9174,16 @@ nsINode* Document::AdoptNode(nsINode& aA
       } while ((doc = doc->GetInProcessParentDocument()));
 
       // Remove from parent.
       nsCOMPtr<nsINode> parent = adoptedNode->GetParentNode();
       if (parent) {
         parent->RemoveChildNode(adoptedNode->AsContent(), true);
       } else {
         MOZ_ASSERT(!adoptedNode->IsInUncomposedDoc());
-
-#ifdef MOZ_XBL
-        // If we're adopting a node that's not in a document, it might still
-        // have a binding applied. Remove the binding from the element now
-        // that it's getting adopted into a new document.
-        // TODO Fully tear down the binding.
-        if (Element* element = Element::FromNode(adoptedNode)) {
-          element->SetXBLBinding(nullptr);
-        }
-#endif
       }
 
       break;
     }
     case DOCUMENT_NODE: {
       rv.Throw(NS_ERROR_DOM_NOT_SUPPORTED_ERR);
       return nullptr;
     }
@@ -14193,25 +14060,16 @@ void Document::AddSizeOfNodeTree(nsINode
     for (nsIContent* anonKid : anonKids) {
       AddSizeOfNodeTree(*anonKid, aWindowSizes);
     }
 
     if (auto* element = Element::FromNode(aNode)) {
       if (ShadowRoot* shadow = element->GetShadowRoot()) {
         AddSizeOfNodeTree(*shadow, aWindowSizes);
       }
-
-#ifdef MOZ_XBL
-      for (nsXBLBinding* binding = element->GetXBLBinding(); binding;
-           binding = binding->GetBaseBinding()) {
-        if (nsIContent* anonContent = binding->GetAnonymousContent()) {
-          AddSizeOfNodeTree(*anonContent, aWindowSizes);
-        }
-      }
-#endif
     }
   }
 
   // NOTE(emilio): If you feel smart and want to change this function to use
   // GetNextNode(), think twice, since you'd need to handle <xbl:content> in a
   // sane way, and kids of <content> won't point to the parent, so we'd never
   // find the root node where we should stop at.
   for (nsIContent* kid = aNode.GetFirstChild(); kid;

--- a/dom/base/Document.h
+++ b/dom/base/Document.h
@@ -80,19 +80,16 @@ namespace mozilla {
 namespace dom {
 class ElementCreationOptionsOrString;
 }  // namespace dom
 }  // namespace mozilla
 #endif  // MOZILLA_INTERNAL_API
 
 class gfxUserFontSet;
 class imgIRequest;
-#ifdef MOZ_XBL
-class nsBindingManager;
-#endif
 class nsCachableElementsByNameNodeList;
 class nsCommandManager;
 class nsContentList;
 class nsIDocShell;
 class nsDocShell;
 class nsDOMNavigationTiming;
 class nsFrameLoader;
 class nsGlobalWindowInner;
@@ -1808,20 +1805,16 @@ class Document : public nsINode,
   nsresult InitFeaturePolicy(nsIChannel* aChannel);
 
   nsresult InitReferrerInfo(nsIChannel* aChannel);
 
   void PostUnblockOnloadEvent();
 
   void DoUnblockOnload();
 
-#ifdef MOZ_XBL
-  void MaybeEndOutermostXBLUpdate();
-#endif
-
   void RetrieveRelevantHeaders(nsIChannel* aChannel);
 
   void TryChannelCharset(nsIChannel* aChannel, int32_t& aCharsetSource,
                          NotNull<const Encoding*>& aEncoding,
                          nsHtml5TreeOpExecutor* aExecutor);
 
   void DispatchContentLoadedEvents();
 
@@ -2389,22 +2382,16 @@ class Document : public nsINode,
   // Triggers an update of <svg:use> element shadow trees.
   void UpdateSVGUseElementShadowTrees() {
     if (mSVGUseElementsNeedingShadowTreeUpdate.IsEmpty()) {
       return;
     }
     DoUpdateSVGUseElementShadowTrees();
   }
 
-#ifdef MOZ_XBL
-  nsBindingManager* BindingManager() const {
-    return mNodeInfoManager->GetBindingManager();
-  }
-#endif
-
   /**
    * Only to be used inside Gecko, you can't really do anything with the
    * pointer outside Gecko anyway.
    */
   nsNodeInfoManager* NodeInfoManager() const { return mNodeInfoManager; }
 
   /**
    * Reset the document using the given channel and loadgroup.  This works
@@ -5289,19 +5276,16 @@ class Document : public nsINode,
 
   CSSCoord mMinWidth;
   CSSCoord mMaxWidth;
   CSSCoord mMinHeight;
   CSSCoord mMaxHeight;
 
   RefPtr<EventListenerManager> mListenerManager;
 
-#ifdef MOZ_XBL
-  nsCOMPtr<nsIRunnable> mMaybeEndOutermostXBLUpdateRunner;
-#endif
   nsCOMPtr<nsIRequest> mOnloadBlocker;
 
   nsTArray<RefPtr<StyleSheet>> mAdditionalSheets[AdditionalSheetTypeCount];
 
   // Member to store out last-selected stylesheet set.
   nsString mLastStyleSheetSet;
   nsString mPreferredStyleSheetSet;
 

--- a/dom/base/Element.cpp
+++ b/dom/base/Element.cpp
@@ -11,16 +11,17 @@
  */
 
 #include "mozilla/dom/ElementInlines.h"
 
 #include "AnimationCommon.h"
 #include "mozilla/DebugOnly.h"
 #include "mozilla/StaticPrefs_dom.h"
 #include "mozilla/StaticPrefs_layout.h"
+#include "mozilla/StaticPrefs_full_screen_api.h"
 #include "mozilla/dom/Animation.h"
 #include "mozilla/dom/Attr.h"
 #include "mozilla/dom/BindContext.h"
 #include "mozilla/dom/Flex.h"
 #include "mozilla/dom/Grid.h"
 #include "mozilla/dom/Link.h"
 #include "mozilla/dom/MutationObservers.h"
 #include "mozilla/dom/ScriptLoader.h"
@@ -89,22 +90,16 @@
 #  include "nsXULElement.h"
 #endif /* MOZ_XUL */
 #include "SVGElement.h"
 #include "nsFrameSelection.h"
 #ifdef DEBUG
 #  include "nsRange.h"
 #endif
 
-#ifdef MOZ_XBL
-#  include "nsXBLPrototypeBinding.h"
-#  include "nsBindingManager.h"
-#  include "nsXBLBinding.h"
-#  include "nsXBLService.h"
-#endif
 #include "nsPIDOMWindow.h"
 #include "mozilla/dom/DOMRect.h"
 #include "nsSVGUtils.h"
 #include "nsLayoutUtils.h"
 #include "nsGkAtoms.h"
 #include "ChildIterator.h"
 
 #include "nsIDOMEventListener.h"
@@ -262,23 +257,17 @@ Element::QueryInterface(REFNSIID aIID, v
   }
 
   NS_ASSERTION(aInstancePtr, "QueryInterface requires a non-NULL destination!");
   nsresult rv = FragmentOrElement::QueryInterface(aIID, aInstancePtr);
   if (NS_SUCCEEDED(rv)) {
     return NS_OK;
   }
 
-#if MOZ_XBL
-  // Give the binding manager a chance to get an interface for this element.
-  return OwnerDoc()->BindingManager()->GetBindingImplementation(this, aIID,
-                                                                aInstancePtr);
-#else
   return NS_NOINTERFACE;
-#endif
 }
 
 EventStates Element::IntrinsicState() const {
   return IsEditable() ? NS_EVENT_STATE_MOZ_READWRITE
                       : NS_EVENT_STATE_MOZ_READONLY;
 }
 
 void Element::NotifyStateChange(EventStates aStates) {
@@ -377,58 +366,16 @@ void Element::Focus(const FocusOptions& 
 
 void Element::SetTabIndex(int32_t aTabIndex, mozilla::ErrorResult& aError) {
   nsAutoString value;
   value.AppendInt(aTabIndex);
 
   SetAttr(nsGkAtoms::tabindex, value, aError);
 }
 
-#ifdef MOZ_XBL
-void Element::SetXBLBinding(nsXBLBinding* aBinding,
-                            nsBindingManager* aOldBindingManager) {
-  nsBindingManager* bindingManager;
-  if (aOldBindingManager) {
-    MOZ_ASSERT(!aBinding,
-               "aOldBindingManager should only be provided "
-               "when removing a binding.");
-    bindingManager = aOldBindingManager;
-  } else {
-    bindingManager = OwnerDoc()->BindingManager();
-  }
-
-  // After this point, aBinding will be the most-derived binding for aContent.
-  // If we already have a binding for aContent, make sure to
-  // remove it from the attached stack.  Otherwise we might end up firing its
-  // constructor twice (if aBinding inherits from it) or firing its constructor
-  // after aContent has been deleted (if aBinding is null and the content node
-  // dies before we process mAttachedStack).
-  RefPtr<nsXBLBinding> oldBinding = GetXBLBinding();
-  if (oldBinding) {
-    bindingManager->RemoveFromAttachedQueue(oldBinding);
-  }
-
-  if (aBinding) {
-    SetFlags(NODE_MAY_BE_IN_BINDING_MNGR);
-    nsExtendedDOMSlots* slots = ExtendedDOMSlots();
-    slots->mXBLBinding = aBinding;
-    bindingManager->AddBoundContent(this);
-  } else {
-    nsExtendedDOMSlots* slots = GetExistingExtendedDOMSlots();
-    if (slots) {
-      slots->mXBLBinding = nullptr;
-    }
-    bindingManager->RemoveBoundContent(this);
-    if (oldBinding) {
-      oldBinding->SetBoundElement(nullptr);
-    }
-  }
-}
-#endif
-
 void Element::SetShadowRoot(ShadowRoot* aShadowRoot) {
   nsExtendedDOMSlots* slots = ExtendedDOMSlots();
   slots->mShadowRoot = aShadowRoot;
 }
 
 void Element::Blur(mozilla::ErrorResult& aError) {
   if (!ShouldBlur(this)) {
     return;
@@ -1060,21 +1007,17 @@ already_AddRefed<ShadowRoot> Element::At
     aError.Throw(NS_ERROR_DOM_NOT_SUPPORTED_ERR);
     return nullptr;
   }
 
   /**
    * 3. If context object is a shadow host, then throw
    *    an "InvalidStateError" DOMException.
    */
-  if (GetShadowRoot()
-#ifdef MOZ_XBL
-      || GetXBLBinding()
-#endif
-  ) {
+  if (GetShadowRoot()) {
     aError.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
     return nullptr;
   }
 
   if (StaticPrefs::dom_webcomponents_shadowdom_report_usage()) {
     OwnerDoc()->ReportShadowDOMUsage();
   }
 
@@ -1591,29 +1534,16 @@ nsresult Element::BindToTree(BindContext
   //  because it has to happen after updating the parent pointer, but before
   //  recursively binding the kids.
   if (IsHTMLElement()) {
     SetDirOnBind(this, nsIContent::FromNode(aParent));
   }
 
   UpdateEditableState(false);
 
-#ifdef MOZ_XBL
-  // If we had a pre-existing XBL binding, we might have anonymous children that
-  // also need to be told that they are moving.
-  if (HasFlag(NODE_MAY_BE_IN_BINDING_MNGR)) {
-    nsXBLBinding* binding =
-        aContext.OwnerDoc().BindingManager()->GetBindingWithContent(this);
-
-    if (binding) {
-      binding->BindAnonymousContent(binding->GetAnonymousContent(), this);
-    }
-  }
-#endif
-
   // Call BindToTree on shadow root children.
   nsresult rv;
   if (ShadowRoot* shadowRoot = GetShadowRoot()) {
     rv = shadowRoot->Bind();
     NS_ENSURE_SUCCESS(rv, rv);
   }
 
   // Now recurse into our kids. Ensure this happens after binding the shadow
@@ -1684,44 +1614,16 @@ nsresult Element::BindToTree(BindContext
              "Bound to wrong binding parent");
   MOZ_ASSERT(aParent.IsInUncomposedDoc() == IsInUncomposedDoc());
   MOZ_ASSERT(aParent.IsInComposedDoc() == IsInComposedDoc());
   MOZ_ASSERT(aParent.IsInShadowTree() == IsInShadowTree());
   MOZ_ASSERT(aParent.SubtreeRoot() == SubtreeRoot());
   return NS_OK;
 }
 
-#ifdef MOZ_XBL
-RemoveFromBindingManagerRunnable::RemoveFromBindingManagerRunnable(
-    nsBindingManager* aManager, nsIContent* aContent, Document* aDoc)
-    : mozilla::Runnable("dom::RemoveFromBindingManagerRunnable"),
-      mManager(aManager),
-      mContent(aContent),
-      mDoc(aDoc) {}
-
-RemoveFromBindingManagerRunnable::~RemoveFromBindingManagerRunnable() {}
-
-NS_IMETHODIMP
-RemoveFromBindingManagerRunnable::Run() {
-  // It may be the case that the element was removed from the
-  // DOM, causing this runnable to be created, then inserted back
-  // into the document before the this runnable had a chance to
-  // tear down the binding. Only tear down the binding if the element
-  // is still no longer in the DOM. nsXBLService::LoadBinding tears
-  // down the old binding if the element is inserted back into the
-  // DOM and loads a different binding.
-  if (!mContent->IsInComposedDoc()) {
-    mManager->RemovedFromDocumentInternal(mContent, mDoc,
-                                          nsBindingManager::eRunDtor);
-  }
-
-  return NS_OK;
-}
-#endif
-
 bool WillDetachFromShadowOnUnbind(const Element& aElement, bool aNullParent) {
   // If our parent still is in a shadow tree by now, and we're not removing
   // ourselves from it, then we're still going to be in a shadow tree after
   // this.
   return aElement.IsInShadowTree() &&
          (aNullParent || !aElement.GetParent()->IsInShadowTree());
 }
 
@@ -1859,32 +1761,16 @@ void Element::UnbindFromTree(bool aNullP
       slots->mBindingParent = nullptr;
     }
     if (aNullParent || !mParent->IsInShadowTree()) {
       slots->mContainingShadow = nullptr;
     }
   }
 
   if (document) {
-#ifdef MOZ_XBL
-    if (HasFlag(NODE_MAY_BE_IN_BINDING_MNGR)) {
-      // Notify XBL- & nsIAnonymousContentCreator-generated anonymous content
-      // that the document is changing.
-      nsContentUtils::AddScriptRunner(new RemoveFromBindingManagerRunnable(
-          document->BindingManager(), this, document));
-      nsXBLBinding* binding =
-          document->BindingManager()->GetBindingWithContent(this);
-      if (binding) {
-        nsXBLBinding::UnbindAnonymousContent(document,
-                                             binding->GetAnonymousContent(),
-                                             /* aNullParent */ false);
-      }
-    }
-#endif
-
     // Disconnected must be enqueued whenever a connected custom element becomes
     // disconnected.
     CustomElementData* data = GetCustomElementData();
     if (data) {
       if (data->mState == CustomElementData::State::eCustom) {
         nsContentUtils::EnqueueLifecycleCallback(Document::eDisconnected, this);
       } else {
         // Remove an unresolved custom element that is a candidate for upgrade
@@ -2403,25 +2289,16 @@ nsresult Element::SetAttrAndNotify(
       oldValue = nullptr;
     }
   } else {
     // No need to conditionally assign null here. If there was no previously
     // set value for the attribute, aOldValue will already be null.
     oldValue = aOldValue;
   }
 
-#ifdef MOZ_XBL
-  if (aComposedDocument) {
-    RefPtr<nsXBLBinding> binding = GetXBLBinding();
-    if (binding) {
-      binding->AttributeChanged(aName, aNamespaceID, false, aNotify);
-    }
-  }
-#endif
-
   if (HasElementCreatedFromPrototypeAndHasUnmodifiedL10n() &&
       aNamespaceID == kNameSpaceID_None &&
       (aName == nsGkAtoms::datal10nid || aName == nsGkAtoms::datal10nargs)) {
     ClearElementCreatedFromPrototypeAndHasUnmodifiedL10n();
     if (aComposedDocument) {
       aComposedDocument->mL10nProtoElements.Remove(this);
     }
   }
@@ -2512,16 +2389,22 @@ bool Element::ParseAttribute(int32_t aNa
   }
 
   if (aNamespaceID == kNameSpaceID_None) {
     if (aAttribute == nsGkAtoms::_class || aAttribute == nsGkAtoms::part) {
       aResult.ParseAtomArray(aValue);
       return true;
     }
 
+    if (aAttribute == nsGkAtoms::exportparts &&
+        StaticPrefs::layout_css_shadow_parts_enabled()) {
+      aResult.ParsePartMapping(aValue);
+      return true;
+    }
+
     if (aAttribute == nsGkAtoms::id) {
       // Store id as an atom.  id="" means that the element has no id,
       // not that it has an emptystring as the id.
       if (aValue.IsEmpty()) {
         return false;
       }
       aResult.ParseAtom(aValue);
       return true;
@@ -2715,25 +2598,16 @@ nsresult Element::UnsetAttr(int32_t aNam
   }
 
   nsAttrValue oldValue;
   rv = mAttrs.RemoveAttrAt(index, oldValue);
   NS_ENSURE_SUCCESS(rv, rv);
 
   PostIdMaybeChange(aNameSpaceID, aName, nullptr);
 
-#ifdef MOZ_XBL
-  if (document) {
-    RefPtr<nsXBLBinding> binding = GetXBLBinding();
-    if (binding) {
-      binding->AttributeChanged(aName, aNameSpaceID, true, aNotify);
-    }
-  }
-#endif
-
   CustomElementDefinition* definition = GetCustomElementDefinition();
   // Only custom element which is in `custom` state could get the
   // CustomElementDefinition.
   if (definition && definition->IsInObservedAttributeList(aName)) {
     nsAutoString ns;
     nsContentUtils::NameSpaceManager()->GetNameSpaceURI(aNameSpaceID, ns);
 
     RefPtr<nsAtom> oldValueAtom = oldValue.GetAsAtom();
@@ -2843,63 +2717,16 @@ void Element::List(FILE* out, int32_t aI
     for (; child; child = child->GetNextSibling()) {
       child->List(out, aIndent + 1);
     }
 
     for (indent = aIndent; --indent >= 0;) fputs("  ", out);
   }
 
   fputs(">\n", out);
-
-#  ifdef MOZ_XBL
-  Element* nonConstThis = const_cast<Element*>(this);
-
-  // XXX sXBL/XBL2 issue! Owner or current document?
-  Document* document = OwnerDoc();
-
-  // Note: not listing nsIAnonymousContentCreator-created content...
-
-  nsBindingManager* bindingManager = document->BindingManager();
-  nsINodeList* anonymousChildren =
-      bindingManager->GetAnonymousNodesFor(nonConstThis);
-
-  if (anonymousChildren) {
-    uint32_t length = anonymousChildren->Length();
-
-    for (indent = aIndent; --indent >= 0;) fputs("  ", out);
-    fputs("anonymous-children<\n", out);
-
-    for (uint32_t i = 0; i < length; ++i) {
-      nsIContent* child = anonymousChildren->Item(i);
-      child->List(out, aIndent + 1);
-    }
-
-    for (indent = aIndent; --indent >= 0;) fputs("  ", out);
-    fputs(">\n", out);
-
-    bool outHeader = false;
-    ExplicitChildIterator iter(nonConstThis);
-    for (nsIContent* child = iter.GetNextChild(); child;
-         child = iter.GetNextChild()) {
-      if (!outHeader) {
-        outHeader = true;
-
-        for (indent = aIndent; --indent >= 0;) fputs("  ", out);
-        fputs("content-list<\n", out);
-      }
-
-      child->List(out, aIndent + 1);
-    }
-
-    if (outHeader) {
-      for (indent = aIndent; --indent >= 0;) fputs("  ", out);
-      fputs(">\n", out);
-    }
-  }
-#  endif
 }
 
 void Element::DumpContent(FILE* out, int32_t aIndent, bool aDumpAll) const {
   int32_t indent;
   for (indent = aIndent; --indent >= 0;) fputs("  ", out);
 
   const nsString& buf = mNodeInfo->QualifiedName();
   fputs("<", out);
@@ -3909,23 +3736,16 @@ template <class T>
 void Element::GetCustomInterface(nsGetterAddRefs<T> aResult) {
   nsCOMPtr<nsISupports> iface = CustomElementRegistry::CallGetCustomInterface(
       this, NS_GET_TEMPLATE_IID(T));
   if (iface) {
     if (NS_SUCCEEDED(CallQueryInterface(iface, static_cast<T**>(aResult)))) {
       return;
     }
   }
-
-#ifdef MOZ_XBL
-  // Otherwise, check the binding manager to see if it implements the interface
-  // for this element.
-  OwnerDoc()->BindingManager()->GetBindingImplementation(
-      this, NS_GET_TEMPLATE_IID(T), aResult);
-#endif
 }
 
 void Element::ClearServoData(Document* aDoc) {
   MOZ_ASSERT(aDoc);
   if (HasServoData()) {
     Servo_Element_ClearData(this);
   } else {
     UnsetFlags(kAllServoDescendantBits | NODE_NEEDS_FRAME);

--- a/dom/base/Element.h
+++ b/dom/base/Element.h
@@ -219,34 +219,16 @@ class Element : public FragmentOrElement
    */
   int32_t TabIndex();
 
   /**
    * Set tabIndex value to this element.
    */
   void SetTabIndex(int32_t aTabIndex, mozilla::ErrorResult& aError);
 
-#ifdef MOZ_XBL
-  /**
-   * Sets or unsets an XBL binding for this element. Setting a
-   * binding on an element that already has a binding will remove the
-   * old binding.
-   *
-   * @param aBinding The binding to bind to this content. If nullptr is
-   *        provided as the argument, then existing binding will be
-   *        removed.
-   *
-   * @param aOldBindingManager The old binding manager that contains
-   *                           this content if this content was adopted
-   *                           to another document.
-   */
-  void SetXBLBinding(nsXBLBinding* aBinding,
-                     nsBindingManager* aOldBindingManager = nullptr);
-#endif
-
   /**
    * Sets the ShadowRoot binding for this element. The contents of the
    * binding is rendered in place of this node's children.
    *
    * @param aShadowRoot The ShadowRoot to be bound to this element.
    */
   void SetShadowRoot(ShadowRoot* aShadowRoot);
 
@@ -1970,32 +1952,16 @@ class Element : public FragmentOrElement
   // descendants of display: none elements.
   mozilla::RustCell<ServoNodeData*> mServoData;
 
  protected:
   // Array containing all attributes for this element
   AttrArray mAttrs;
 };
 
-#ifdef MOZ_XBL
-class RemoveFromBindingManagerRunnable : public mozilla::Runnable {
- public:
-  RemoveFromBindingManagerRunnable(nsBindingManager* aManager,
-                                   nsIContent* aContent, Document* aDoc);
-
-  NS_IMETHOD Run() override;
-
- private:
-  virtual ~RemoveFromBindingManagerRunnable();
-  RefPtr<nsBindingManager> mManager;
-  RefPtr<nsIContent> mContent;
-  RefPtr<Document> mDoc;
-};
-#endif
-
 NS_DEFINE_STATIC_IID_ACCESSOR(Element, NS_ELEMENT_IID)
 
 inline bool Element::HasAttr(int32_t aNameSpaceID, const nsAtom* aName) const {
   NS_ASSERTION(nullptr != aName, "must have attribute name");
   NS_ASSERTION(aNameSpaceID != kNameSpaceID_Unknown,
                "must have a real namespace ID!");
 
   return mAttrs.IndexOfAttr(aName, aNameSpaceID) >= 0;