--- a/accessible/generic/Accessible.cpp
+++ b/accessible/generic/Accessible.cpp
@@ -27,17 +27,16 @@
 #include "StyleInfo.h"
 #include "TableAccessible.h"
 #include "TableCellAccessible.h"
 #include "TreeWalker.h"
 #include "XULDocument.h"
 
 #include "nsIDOMElement.h"
 #include "nsIDOMXULButtonElement.h"
-#include "nsIDOMXULElement.h"
 #include "nsIDOMXULLabelElement.h"
 #include "nsIDOMXULSelectCntrlEl.h"
 #include "nsIDOMXULSelectCntrlItemEl.h"
 #include "nsINodeList.h"
 #include "nsPIDOMWindow.h"
 
 #include "nsIDocument.h"
 #include "nsIContent.h"

--- a/accessible/generic/FormControlAccessible.cpp
+++ b/accessible/generic/FormControlAccessible.cpp
@@ -4,17 +4,16 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 // NOTE: alphabetically ordered
 
 #include "FormControlAccessible.h"
 #include "Role.h"
 
 #include "mozilla/FloatingPoint.h"
-#include "nsIDOMXULElement.h"
 #include "nsIDOMXULControlElement.h"
 
 using namespace mozilla::a11y;
 
 ////////////////////////////////////////////////////////////////////////////////
 // ProgressMeterAccessible
 ////////////////////////////////////////////////////////////////////////////////
 

--- a/accessible/tests/mochitest/common.js
+++ b/accessible/tests/mochitest/common.js
@@ -43,17 +43,16 @@ const nsIAccessibleTraversalRule = Ci.ns
 const nsIAccessibleValue = Ci.nsIAccessibleValue;
 
 const nsIObserverService = Ci.nsIObserverService;
 
 const nsIDOMDocument = Ci.nsIDOMDocument;
 const nsIDOMEvent = Ci.nsIDOMEvent;
 const nsIDOMNode = Ci.nsIDOMNode;
 const nsIDOMWindow = Ci.nsIDOMWindow;
-const nsIDOMXULElement = Ci.nsIDOMXULElement;
 
 const nsIPropertyElement = Ci.nsIPropertyElement;
 
 // //////////////////////////////////////////////////////////////////////////////
 // OS detect
 
 const MAC = (navigator.platform.includes("Mac"));
 const LINUX = (navigator.platform.includes("Linux"));

--- a/accessible/tests/mochitest/events.js
+++ b/accessible/tests/mochitest/events.js
@@ -1064,26 +1064,26 @@ function synthClick(aNodeOrID, aCheckerO
     if (targetNode instanceof nsIDOMDocument) {
       targetNode =
         this.DOMNode.body ? this.DOMNode.body : this.DOMNode.documentElement;
     }
 
     // Scroll the node into view, otherwise synth click may fail.
     if (isHTMLElement(targetNode)) {
       targetNode.scrollIntoView(true);
-    } else if (targetNode instanceof nsIDOMXULElement) {
+    } else if (ChromeUtils.getClassName(targetNode) == "XULElement") {
       var targetAcc = getAccessible(targetNode);
       targetAcc.scrollTo(SCROLL_TYPE_ANYWHERE);
     }
 
     var x = 1, y = 1;
     if (aArgs && ("where" in aArgs) && aArgs.where == "right") {
       if (isHTMLElement(targetNode))
         x = targetNode.offsetWidth - 1;
-      else if (targetNode instanceof nsIDOMXULElement)
+    else if (ChromeUtils.getClassName(targetNode) == "XULElement")
         x = targetNode.boxObject.width - 1;
     }
     synthesizeMouse(targetNode, x, y, aArgs ? aArgs : {});
   };
 
   this.finalCheck = function synthClick_finalCheck() {
     // Scroll top window back.
     window.top.scrollTo(0, 0);

--- a/accessible/xul/XULMenuAccessible.cpp
+++ b/accessible/xul/XULMenuAccessible.cpp
@@ -9,17 +9,16 @@
 #include "nsAccessibilityService.h"
 #include "nsAccUtils.h"
 #include "DocAccessible.h"
 #include "Role.h"
 #include "States.h"
 #include "XULFormControlAccessible.h"
 
 #include "nsIDOMElement.h"
-#include "nsIDOMXULElement.h"
 #include "nsIMutableArray.h"
 #include "nsIDOMXULContainerElement.h"
 #include "nsIDOMXULSelectCntrlItemEl.h"
 #include "nsIDOMXULMultSelectCntrlEl.h"
 #include "nsIServiceManager.h"
 #include "nsIPresShell.h"
 #include "nsIContent.h"
 #include "nsMenuBarFrame.h"

--- a/accessible/xul/XULSelectControlAccessible.cpp
+++ b/accessible/xul/XULSelectControlAccessible.cpp
@@ -8,17 +8,16 @@
 
 #include "nsAccessibilityService.h"
 #include "DocAccessible.h"
 
 #include "nsIDOMXULContainerElement.h"
 #include "nsIDOMXULSelectCntrlItemEl.h"
 #include "nsIDOMXULMultSelectCntrlEl.h"
 #include "nsIDOMElement.h"
-#include "nsIDOMXULElement.h"
 #include "nsIMutableArray.h"
 #include "nsIServiceManager.h"
 
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/KeyboardEventBinding.h"
 
 using namespace mozilla;
 using namespace mozilla::a11y;

--- a/accessible/xul/XULTreeAccessible.cpp
+++ b/accessible/xul/XULTreeAccessible.cpp
@@ -19,17 +19,16 @@
 #include "XULTreeGridAccessible.h"
 #include "nsQueryObject.h"
 
 #include "nsComponentManagerUtils.h"
 #include "nsIAccessibleRelation.h"
 #include "nsIAutoCompleteInput.h"
 #include "nsIAutoCompletePopup.h"
 #include "nsIBoxObject.h"
-#include "nsIDOMXULElement.h"
 #include "nsIDOMXULMenuListElement.h"
 #include "nsIDOMXULMultSelectCntrlEl.h"
 #include "nsIDOMXULTreeElement.h"
 #include "nsITreeSelection.h"
 #include "nsIMutableArray.h"
 #include "nsTreeBodyFrame.h"
 #include "nsTreeColumns.h"
 #include "nsTreeUtils.h"

--- a/browser/base/content/test/contextMenu/browser_contextmenu_linkopen.js
+++ b/browser/base/content/test/contextMenu/browser_contextmenu_linkopen.js
@@ -13,25 +13,25 @@ async function activateContextAndWaitFor
   switch (where) {
     case "tab":
       contextMenuItem += "intab";
       openPromise = BrowserTestUtils.waitForNewTab(gBrowser, TEST_LINK, false);
       closeMethod = async (tab) => BrowserTestUtils.removeTab(tab);
       break;
     case "privatewindow":
       contextMenuItem += "private";
-      openPromise = BrowserTestUtils.waitForNewWindow(TEST_LINK).then(win => {
+      openPromise = BrowserTestUtils.waitForNewWindow({url: TEST_LINK}).then(win => {
         ok(PrivateBrowsingUtils.isWindowPrivate(win), "Should have opened a private window.");
         return win;
       });
       closeMethod = async (win) => BrowserTestUtils.closeWindow(win);
       break;
     case "window":
       // No contextMenuItem suffix for normal new windows;
-      openPromise = BrowserTestUtils.waitForNewWindow(TEST_LINK).then(win => {
+      openPromise = BrowserTestUtils.waitForNewWindow({url: TEST_LINK}).then(win => {
         ok(!PrivateBrowsingUtils.isWindowPrivate(win), "Should have opened a normal window.");
         return win;
       });
       closeMethod = async (win) => BrowserTestUtils.closeWindow(win);
       break;
   }
   let contextMenu = document.getElementById("contentAreaContextMenu");
   is(contextMenu.state, "closed", "checking if popup is closed");

--- a/browser/base/content/test/general/browser_newTabDrop.js
+++ b/browser/base/content/test/general/browser_newTabDrop.js
@@ -1,166 +1,219 @@
+const ANY_URL = undefined;
+
 registerCleanupFunction(async function cleanup() {
   while (gBrowser.tabs.length > 1) {
     BrowserTestUtils.removeTab(gBrowser.tabs[gBrowser.tabs.length - 1]);
   }
   Services.search.currentEngine = originalEngine;
   let engine = Services.search.getEngineByName("MozSearch");
   Services.search.removeEngine(engine);
 });
 
 let originalEngine;
 add_task(async function test_setup() {
+  // This test opens multiple tabs and some confirm dialogs, that takes long.
+  requestLongerTimeout(2);
+
   // Stop search-engine loads from hitting the network
   Services.search.addEngineWithDetails("MozSearch", "", "", "", "GET",
                                        "http://example.com/?q={searchTerms}");
   let engine = Services.search.getEngineByName("MozSearch");
   originalEngine = Services.search.currentEngine;
   Services.search.currentEngine = engine;
 });
 
 // New Tab Button opens any link.
-add_task(async function() { await dropText("mochi.test/first", 1); });
-add_task(async function() { await dropText("javascript:'bad'", 1); });
-add_task(async function() { await dropText("jAvascript:'bad'", 1); });
-add_task(async function() { await dropText("mochi.test/second", 1); });
-add_task(async function() { await dropText("data:text/html,bad", 1); });
-add_task(async function() { await dropText("mochi.test/third", 1); });
+add_task(async function single_url() {
+  await dropText("mochi.test/first",
+                 ["http://www.mochi.test/first"]);
+});
+add_task(async function single_javascript() {
+  await dropText("javascript:'bad'",
+                 ["javascript:'bad'"]);
+});
+add_task(async function single_javascript_capital() {
+  await dropText("jAvascript:'bad'",
+                 ["javascript:'bad'"]);
+});
+add_task(async function single_url2() {
+  await dropText("mochi.test/second",
+                 ["http://www.mochi.test/second"]);
+});
+add_task(async function single_data_url() {
+  await dropText("data:text/html,bad",
+                 ["data:text/html,bad"]);
+});
+add_task(async function single_url3() {
+  await dropText("mochi.test/third",
+                 ["http://www.mochi.test/third"]);
+});
 
 // Single text/plain item, with multiple links.
-add_task(async function() { await dropText("mochi.test/1\nmochi.test/2", 2); });
-add_task(async function() { await dropText("javascript:'bad1'\nmochi.test/3", 2); });
-add_task(async function() { await dropText("mochi.test/4\ndata:text/html,bad1", 2); });
+add_task(async function multiple_urls() {
+  await dropText("mochi.test/1\nmochi.test/2",
+                 [
+                   "http://www.mochi.test/1",
+                   "http://www.mochi.test/2",
+                 ]);
+});
+add_task(async function multiple_urls_javascript() {
+  await dropText("javascript:'bad1'\nmochi.test/3",
+                 [
+                   "javascript:'bad1'",
+                   "http://www.mochi.test/3",
+                 ]);
+});
+add_task(async function multiple_urls_data() {
+  await dropText("mochi.test/4\ndata:text/html,bad1",
+                 [
+                   "http://www.mochi.test/4",
+                   "data:text/html,bad1",
+                 ]);
+});
 
 // Multiple text/plain items, with single and multiple links.
-add_task(async function() {
+add_task(async function multiple_items_single_and_multiple_links() {
   await drop([[{type: "text/plain",
                 data: "mochi.test/5"}],
               [{type: "text/plain",
-                data: "mochi.test/6\nmochi.test/7"}]], 3);
+                data: "mochi.test/6\nmochi.test/7"}]],
+             [
+               "http://www.mochi.test/5",
+               "http://www.mochi.test/6",
+               "http://www.mochi.test/7",
+             ]);
 });
 
 // Single text/x-moz-url item, with multiple links.
 // "text/x-moz-url" has titles in even-numbered lines.
-add_task(async function() {
+add_task(async function single_moz_url_multiple_links() {
   await drop([[{type: "text/x-moz-url",
-                data: "mochi.test/8\nTITLE8\nmochi.test/9\nTITLE9"}]], 2);
+                data: "mochi.test/8\nTITLE8\nmochi.test/9\nTITLE9"}]],
+             [
+               "http://www.mochi.test/8",
+               "http://www.mochi.test/9",
+             ]);
 });
 
 // Single item with multiple types.
-add_task(async function() {
+add_task(async function single_item_multiple_types() {
   await drop([[{type: "text/plain",
                 data: "mochi.test/10"},
                {type: "text/x-moz-url",
-                data: "mochi.test/11\nTITLE11"}]], 1);
+                data: "mochi.test/11\nTITLE11"}]],
+             ["http://www.mochi.test/11"]);
 });
 
 // Warn when too many URLs are dropped.
 add_task(async function multiple_tabs_under_max() {
   let urls = [];
   for (let i = 0; i < 5; i++) {
     urls.push("mochi.test/multi" + i);
   }
-  await dropText(urls.join("\n"), 5);
+  await dropText(urls.join("\n"),
+                 [
+                   "http://www.mochi.test/multi0",
+                   "http://www.mochi.test/multi1",
+                   "http://www.mochi.test/multi2",
+                   "http://www.mochi.test/multi3",
+                   "http://www.mochi.test/multi4",
+                 ]);
 });
 add_task(async function multiple_tabs_over_max_accept() {
   await pushPrefs(["browser.tabs.maxOpenBeforeWarn", 4]);
 
   let confirmPromise = BrowserTestUtils.promiseAlertDialog("accept");
 
   let urls = [];
   for (let i = 0; i < 5; i++) {
     urls.push("mochi.test/accept" + i);
   }
-  await dropText(urls.join("\n"), 5);
+  await dropText(urls.join("\n"),
+                 [
+                   "http://www.mochi.test/accept0",
+                   "http://www.mochi.test/accept1",
+                   "http://www.mochi.test/accept2",
+                   "http://www.mochi.test/accept3",
+                   "http://www.mochi.test/accept4",
+                 ]);
 
   await confirmPromise;
 
   await popPrefs();
 });
 add_task(async function multiple_tabs_over_max_cancel() {
   await pushPrefs(["browser.tabs.maxOpenBeforeWarn", 4]);
 
   let confirmPromise = BrowserTestUtils.promiseAlertDialog("cancel");
 
   let urls = [];
   for (let i = 0; i < 5; i++) {
     urls.push("mochi.test/cancel" + i);
   }
-  await dropText(urls.join("\n"), 0);
+  await dropText(urls.join("\n"), []);
 
   await confirmPromise;
 
   await popPrefs();
 });
 
 // Open URLs ignoring non-URL.
 add_task(async function multiple_urls() {
   await dropText(`
     mochi.test/urls0
     mochi.test/urls1
     mochi.test/urls2
     non url0
     mochi.test/urls3
     non url1
     non url2
-`, 4);
+`, [
+  "http://www.mochi.test/urls0",
+  "http://www.mochi.test/urls1",
+  "http://www.mochi.test/urls2",
+  "http://www.mochi.test/urls3",
+]);
 });
 
 // Open single search if there's no URL.
 add_task(async function multiple_text() {
   await dropText(`
     non url0
     non url1
     non url2
-`, 1);
+`, [
+  ANY_URL
+]);
 });
 
-function dropText(text, expectedTabOpenCount = 0) {
-  return drop([[{type: "text/plain", data: text}]], expectedTabOpenCount);
+function dropText(text, expectedURLs) {
+  return drop([[{type: "text/plain", data: text}]], expectedURLs);
 }
 
-async function drop(dragData, expectedTabOpenCount = 0) {
+async function drop(dragData, expectedURLs) {
   let dragDataString = JSON.stringify(dragData);
-  info(`Starting test for datagData:${dragDataString}; expectedTabOpenCount:${expectedTabOpenCount}`);
+  info(`Starting test for dragData:${dragDataString}; expectedURLs.length:${expectedURLs.length}`);
   let EventUtils = {};
   Services.scriptloader.loadSubScript("chrome://mochikit/content/tests/SimpleTest/EventUtils.js", EventUtils);
 
   // Since synthesizeDrop triggers the srcElement, need to use another button.
   let dragSrcElement = document.getElementById("downloads-button");
   ok(dragSrcElement, "Downloads button exists");
   let newTabButton = document.getElementById("new-tab-button");
   ok(newTabButton, "New Tab button exists");
 
   let awaitDrop = BrowserTestUtils.waitForEvent(newTabButton, "drop");
-  let actualTabOpenCount = 0;
-  let openedTabs = [];
-  let promiseTabsOpen = null;
-  let resolve = null;
-  let handler = function(event) {
-    openedTabs.push(event.target);
-    actualTabOpenCount++;
-    if (actualTabOpenCount == expectedTabOpenCount && resolve) {
-      resolve();
-    }
-  };
-  gBrowser.tabContainer.addEventListener("TabOpen", handler);
-  if (expectedTabOpenCount) {
-    promiseTabsOpen = new Promise(r => { resolve = r; });
-  }
+
+  let loadedPromises = expectedURLs.map(
+    url => BrowserTestUtils.waitForNewTab(gBrowser, url, false, true));
 
   EventUtils.synthesizeDrop(dragSrcElement, newTabButton, dragData, "link", window);
 
-  if (promiseTabsOpen) {
-    await promiseTabsOpen;
-    info("Got TabOpen event");
-    for (let tab of openedTabs) {
-      BrowserTestUtils.removeTab(tab);
-    }
+  let tabs = await Promise.all(loadedPromises);
+  for (let tab of tabs) {
+    BrowserTestUtils.removeTab(tab);
   }
 
   await awaitDrop;
   ok(true, "Got drop event");
-
-  gBrowser.tabContainer.removeEventListener("TabOpen", handler);
-  is(actualTabOpenCount, expectedTabOpenCount,
-     "No other tabs are opened");
 }

--- a/browser/base/content/test/general/browser_newWindowDrop.js
+++ b/browser/base/content/test/general/browser_newWindowDrop.js
@@ -26,143 +26,184 @@ add_task(async function test_setup() {
     CustomizableUI.ensureWidgetPlacedInWindow("new-window-button", window);
     registerCleanupFunction(function() {
       CustomizableUI.removeWidgetFromArea("new-window-button");
     });
   }
 });
 
 // New Window Button opens any link.
-add_task(async function() { await dropText("mochi.test/first", 1); });
-add_task(async function() { await dropText("javascript:'bad'", 1); });
-add_task(async function() { await dropText("jAvascript:'bad'", 1); });
-add_task(async function() { await dropText("mochi.test/second", 1); });
-add_task(async function() { await dropText("data:text/html,bad", 1); });
-add_task(async function() { await dropText("mochi.test/third", 1); });
+add_task(async function single_url() {
+  await dropText("mochi.test/first",
+                 ["http://www.mochi.test/first"]);
+});
+add_task(async function single_javascript() {
+  await dropText("javascript:'bad'",
+                 ["about:blank"]);
+});
+add_task(async function single_javascript_capital() {
+  await dropText("jAvascript:'bad'",
+                 ["about:blank"]);
+});
+add_task(async function single_url2() {
+  await dropText("mochi.test/second",
+                 ["http://www.mochi.test/second"]);
+});
+add_task(async function single_data_url() {
+  await dropText("data:text/html,bad",
+                 ["data:text/html,bad"]);
+});
+add_task(async function single_url3() {
+  await dropText("mochi.test/third",
+                 ["http://www.mochi.test/third"]);
+});
 
 // Single text/plain item, with multiple links.
-add_task(async function() { await dropText("mochi.test/1\nmochi.test/2", 2); });
-add_task(async function() { await dropText("javascript:'bad1'\nmochi.test/3", 2); });
-add_task(async function() { await dropText("mochi.test/4\ndata:text/html,bad1", 2); });
+add_task(async function multiple_urls() {
+  await dropText("mochi.test/1\nmochi.test/2",
+                 [
+                   "http://www.mochi.test/1",
+                   "http://www.mochi.test/2",
+                 ]);
+});
+add_task(async function multiple_urls_javascript() {
+  await dropText("javascript:'bad1'\nmochi.test/3",
+                 [
+                   "javascript:'bad1'",
+                   "http://www.mochi.test/3",
+                 ]);
+});
+add_task(async function multiple_urls_data() {
+  await dropText("mochi.test/4\ndata:text/html,bad1",
+                 [
+                   "http://www.mochi.test/4",
+                   "data:text/html,bad1",
+                 ]);
+});
 
 // Multiple text/plain items, with single and multiple links.
-add_task(async function() {
+add_task(async function multiple_items_single_and_multiple_links() {
   await drop([[{type: "text/plain",
                 data: "mochi.test/5"}],
               [{type: "text/plain",
-                data: "mochi.test/6\nmochi.test/7"}]], 3);
+                data: "mochi.test/6\nmochi.test/7"}]],
+             [
+               "http://www.mochi.test/5",
+               "http://www.mochi.test/6",
+               "http://www.mochi.test/7",
+             ]);
 });
 
 // Single text/x-moz-url item, with multiple links.
 // "text/x-moz-url" has titles in even-numbered lines.
-add_task(async function() {
+add_task(async function single_moz_url_multiple_links() {
   await drop([[{type: "text/x-moz-url",
-                data: "mochi.test/8\nTITLE8\nmochi.test/9\nTITLE9"}]], 2);
+                data: "mochi.test/8\nTITLE8\nmochi.test/9\nTITLE9"}]],
+             [
+               "http://www.mochi.test/8",
+               "http://www.mochi.test/9",
+             ]);
 });
 
 // Single item with multiple types.
-add_task(async function() {
+add_task(async function single_item_multiple_types() {
   await drop([[{type: "text/plain",
                 data: "mochi.test/10"},
                {type: "text/x-moz-url",
-                data: "mochi.test/11\nTITLE11"}]], 1);
+                data: "mochi.test/11\nTITLE11"}]],
+             ["http://www.mochi.test/11"]);
 });
 
 // Warn when too many URLs are dropped.
 add_task(async function multiple_tabs_under_max() {
   let urls = [];
   for (let i = 0; i < 5; i++) {
     urls.push("mochi.test/multi" + i);
   }
-  await dropText(urls.join("\n"), 5);
+  await dropText(urls.join("\n"),
+                 [
+                   "http://www.mochi.test/multi0",
+                   "http://www.mochi.test/multi1",
+                   "http://www.mochi.test/multi2",
+                   "http://www.mochi.test/multi3",
+                   "http://www.mochi.test/multi4",
+                 ]);
 });
 add_task(async function multiple_tabs_over_max_accept() {
   await pushPrefs(["browser.tabs.maxOpenBeforeWarn", 4]);
 
   let confirmPromise = BrowserTestUtils.promiseAlertDialog("accept");
 
   let urls = [];
   for (let i = 0; i < 5; i++) {
     urls.push("mochi.test/accept" + i);
   }
-  await dropText(urls.join("\n"), 5, true);
+  await dropText(urls.join("\n"),
+                 [
+                   "http://www.mochi.test/accept0",
+                   "http://www.mochi.test/accept1",
+                   "http://www.mochi.test/accept2",
+                   "http://www.mochi.test/accept3",
+                   "http://www.mochi.test/accept4",
+                 ],
+                 true);
 
   await confirmPromise;
 
   await popPrefs();
 });
 add_task(async function multiple_tabs_over_max_cancel() {
   await pushPrefs(["browser.tabs.maxOpenBeforeWarn", 4]);
 
   let confirmPromise = BrowserTestUtils.promiseAlertDialog("cancel");
 
   let urls = [];
   for (let i = 0; i < 5; i++) {
     urls.push("mochi.test/cancel" + i);
   }
-  await dropText(urls.join("\n"), 0, true);
+  await dropText(urls.join("\n"), [], true);
 
   await confirmPromise;
 
   await popPrefs();
 });
 
-function dropText(text, expectedWindowOpenCount = 0,
+function dropText(text, expectedURLs,
                   ignoreFirstWindow = false) {
-  return drop([[{type: "text/plain", data: text}]], expectedWindowOpenCount,
+  return drop([[{type: "text/plain", data: text}]], expectedURLs,
               ignoreFirstWindow);
 }
 
-async function drop(dragData, expectedWindowOpenCount = 0,
+async function drop(dragData, expectedURLs,
                     ignoreFirstWindow = false) {
   let dragDataString = JSON.stringify(dragData);
-  info(`Starting test for datagData:${dragDataString}; expectedWindowOpenCount:${expectedWindowOpenCount}`);
+  info(`Starting test for dragData:${dragDataString}; expectedURLs.length:${expectedURLs.length}`);
   let EventUtils = {};
   Services.scriptloader.loadSubScript("chrome://mochikit/content/tests/SimpleTest/EventUtils.js", EventUtils);
 
   // Since synthesizeDrop triggers the srcElement, need to use another button.
   let dragSrcElement = document.getElementById("downloads-button");
   ok(dragSrcElement, "Downloads button exists");
   let newWindowButton = document.getElementById("new-window-button");
   ok(newWindowButton, "New Window button exists");
 
   let tmp = {};
   ChromeUtils.import("resource://testing-common/TestUtils.jsm", tmp);
 
   let awaitDrop = BrowserTestUtils.waitForEvent(newWindowButton, "drop");
-  let actualWindowOpenCount = 0;
-  let openedWindows = [];
-  let checkCount = function(window) {
-    if (ignoreFirstWindow) {
-      // When dropping too many dialog, the confirm dialog is opened and
-      // domwindowopened notification is dispatched for it, before opening
-      // windows for dropped items.  Ignore it.
-      ignoreFirstWindow = false;
-      return false;
-    }
 
-    // Add observer as soon as domWindow is opened to avoid missing the topic.
-    let awaitStartup = tmp.TestUtils.topicObserved("browser-delayed-startup-finished",
-                                                   subject => subject == window);
-    openedWindows.push([window, awaitStartup]);
-    actualWindowOpenCount++;
-    return actualWindowOpenCount == expectedWindowOpenCount;
-  };
-  let awaitWindowOpen = expectedWindowOpenCount && BrowserTestUtils.domWindowOpened(null, checkCount);
+  let loadedPromises = expectedURLs.map(
+    url => BrowserTestUtils.waitForNewWindow({
+      url,
+      anyWindow: true,
+      maybeErrorPage: true,
+    }));
 
   EventUtils.synthesizeDrop(dragSrcElement, newWindowButton, dragData, "link", window);
 
-  let windowsOpened = false;
-  if (awaitWindowOpen) {
-    await awaitWindowOpen;
-    info("Got Window opened");
-    windowsOpened = true;
-    for (let [window, awaitStartup] of openedWindows.reverse()) {
-      // Wait for startup before closing, to properly close the browser window.
-      await awaitStartup;
-      await BrowserTestUtils.closeWindow(window);
-    }
+  let windows = await Promise.all(loadedPromises);
+  for (let window of windows) {
+    await BrowserTestUtils.closeWindow(window);
   }
-  is(windowsOpened, !!expectedWindowOpenCount, `Windows for ${dragDataString} should only open if any of dropped items are valid`);
 
   await awaitDrop;
   ok(true, "Got drop event");
 }

--- a/browser/base/content/test/general/browser_new_http_window_opened_from_file_tab.js
+++ b/browser/base/content/test/general/browser_new_http_window_opened_from_file_tab.js
@@ -19,33 +19,33 @@ add_task(async function() {
   // Set pref to open in new window.
   Services.prefs.setIntPref("browser.link.open_newwindow", 2);
   registerCleanupFunction(function() {
     Services.prefs.clearUserPref("browser.link.open_newwindow");
   });
 
   // Open new http window from JavaScript in file:// page and check that we get
   // a new window with the correct page and features.
-  let promiseNewWindow = BrowserTestUtils.waitForNewWindow(TEST_HTTP);
+  let promiseNewWindow = BrowserTestUtils.waitForNewWindow({url: TEST_HTTP});
   await ContentTask.spawn(browser, TEST_HTTP, uri => {
     content.open(uri, "_blank");
   });
   let win = await promiseNewWindow;
   registerCleanupFunction(async function() {
     await BrowserTestUtils.closeWindow(win);
   });
   ok(win, "Check that an http window loaded when using window.open.");
   ok(win.menubar.visible,
      "Check that the menu bar on the new window is visible.");
   ok(win.toolbar.visible,
      "Check that the tool bar on the new window is visible.");
 
   // Open new http window from a link in file:// page and check that we get a
   // new window with the correct page and features.
-  promiseNewWindow = BrowserTestUtils.waitForNewWindow(TEST_HTTP);
+  promiseNewWindow = BrowserTestUtils.waitForNewWindow({url: TEST_HTTP});
   await BrowserTestUtils.synthesizeMouseAtCenter("#linkToExample", {}, browser);
   let win2 = await promiseNewWindow;
   registerCleanupFunction(async function() {
     await BrowserTestUtils.closeWindow(win2);
   });
   ok(win2, "Check that an http window loaded when using link.");
   ok(win2.menubar.visible,
      "Check that the menu bar on the new window is visible.");

--- a/browser/base/content/test/general/browser_tabDrop.js
+++ b/browser/base/content/test/general/browser_tabDrop.js
@@ -1,8 +1,10 @@
+const ANY_URL = undefined;
+
 registerCleanupFunction(async function cleanup() {
   while (gBrowser.tabs.length > 1) {
     BrowserTestUtils.removeTab(gBrowser.tabs[gBrowser.tabs.length - 1]);
   }
   Services.search.currentEngine = originalEngine;
   let engine = Services.search.getEngineByName("MozSearch");
   Services.search.removeEngine(engine);
 });
@@ -12,129 +14,172 @@ add_task(async function test_setup() {
   // Stop search-engine loads from hitting the network
   Services.search.addEngineWithDetails("MozSearch", "", "", "", "GET",
                                        "http://example.com/?q={searchTerms}");
   let engine = Services.search.getEngineByName("MozSearch");
   originalEngine = Services.search.currentEngine;
   Services.search.currentEngine = engine;
 });
 
-add_task(async function() { await dropText("mochi.test/first", 1); });
-add_task(async function() { await dropText("javascript:'bad'"); });
-add_task(async function() { await dropText("jAvascript:'bad'"); });
-add_task(async function() { await dropText("search this", 1); });
-add_task(async function() { await dropText("mochi.test/second", 1); });
-add_task(async function() { await dropText("data:text/html,bad"); });
-add_task(async function() { await dropText("mochi.test/third", 1); });
+add_task(async function single_url() {
+  await dropText("mochi.test/first",
+                 ["http://www.mochi.test/first"]);
+});
+add_task(async function single_javascript() {
+  await dropText("javascript:'bad'", []);
+});
+add_task(async function single_javascript_capital() {
+  await dropText("jAvascript:'bad'", []);
+});
+add_task(async function single_search() {
+  await dropText("search this",
+                 [ANY_URL]);
+});
+add_task(async function single_url2() {
+  await dropText("mochi.test/second",
+                 ["http://www.mochi.test/second"]);
+});
+add_task(async function single_data_url() {
+  await dropText("data:text/html,bad", []);
+});
+add_task(async function single_url3() {
+  await dropText("mochi.test/third",
+                 ["http://www.mochi.test/third"]);
+});
 
 // Single text/plain item, with multiple links.
-add_task(async function() { await dropText("mochi.test/1\nmochi.test/2", 2); });
-add_task(async function() { await dropText("javascript:'bad1'\nmochi.test/3", 0); });
-add_task(async function() { await dropText("mochi.test/4\ndata:text/html,bad1", 0); });
+add_task(async function multiple_urls() {
+  await dropText("mochi.test/1\nmochi.test/2",
+                 [
+                   "http://www.mochi.test/1",
+                   "http://www.mochi.test/2",
+                 ]);
+});
+add_task(async function multiple_urls_javascript() {
+  await dropText("javascript:'bad1'\nmochi.test/3", []);
+});
+add_task(async function multiple_urls_data() {
+  await dropText("mochi.test/4\ndata:text/html,bad1", []);
+});
 
 // Multiple text/plain items, with single and multiple links.
-add_task(async function() {
+add_task(async function multiple_items_single_and_multiple_links() {
   await drop([[{type: "text/plain",
                 data: "mochi.test/5"}],
               [{type: "text/plain",
-                data: "mochi.test/6\nmochi.test/7"}]], 3);
+                data: "mochi.test/6\nmochi.test/7"}]],
+             [
+               "http://www.mochi.test/5",
+               "http://www.mochi.test/6",
+               "http://www.mochi.test/7",
+             ]);
 });
 
 // Single text/x-moz-url item, with multiple links.
 // "text/x-moz-url" has titles in even-numbered lines.
-add_task(async function() {
+add_task(async function single_moz_url_multiple_links() {
   await drop([[{type: "text/x-moz-url",
-                data: "mochi.test/8\nTITLE8\nmochi.test/9\nTITLE9"}]], 2);
+                data: "mochi.test/8\nTITLE8\nmochi.test/9\nTITLE9"}]],
+             [
+               "http://www.mochi.test/8",
+               "http://www.mochi.test/9",
+             ]);
 });
 
 // Single item with multiple types.
-add_task(async function() {
+add_task(async function single_item_multiple_types() {
   await drop([[{type: "text/plain",
                 data: "mochi.test/10"},
                {type: "text/x-moz-url",
-                data: "mochi.test/11\nTITLE11"}]], 1);
+                data: "mochi.test/11\nTITLE11"}]],
+             ["http://www.mochi.test/11"]);
 });
 
 // Warn when too many URLs are dropped.
 add_task(async function multiple_tabs_under_max() {
   let urls = [];
   for (let i = 0; i < 5; i++) {
     urls.push("mochi.test/multi" + i);
   }
-  await dropText(urls.join("\n"), 5);
+  await dropText(urls.join("\n"),
+                 [
+                   "http://www.mochi.test/multi0",
+                   "http://www.mochi.test/multi1",
+                   "http://www.mochi.test/multi2",
+                   "http://www.mochi.test/multi3",
+                   "http://www.mochi.test/multi4",
+                 ]);
 });
 add_task(async function multiple_tabs_over_max_accept() {
   await pushPrefs(["browser.tabs.maxOpenBeforeWarn", 4]);
 
   let confirmPromise = BrowserTestUtils.promiseAlertDialog("accept");
 
   let urls = [];
   for (let i = 0; i < 5; i++) {
     urls.push("mochi.test/accept" + i);
   }
-  await dropText(urls.join("\n"), 5, true);
+  await dropText(urls.join("\n"),
+                 [
+                   "http://www.mochi.test/accept0",
+                   "http://www.mochi.test/accept1",
+                   "http://www.mochi.test/accept2",
+                   "http://www.mochi.test/accept3",
+                   "http://www.mochi.test/accept4",
+                 ]);
 
   await confirmPromise;
 
   await popPrefs();
 });
 add_task(async function multiple_tabs_over_max_cancel() {
   await pushPrefs(["browser.tabs.maxOpenBeforeWarn", 4]);
 
   let confirmPromise = BrowserTestUtils.promiseAlertDialog("cancel");
 
   let urls = [];
   for (let i = 0; i < 5; i++) {
     urls.push("mochi.test/cancel" + i);
   }
-  await dropText(urls.join("\n"), 0, true);
+  await dropText(urls.join("\n"), []);
 
   await confirmPromise;
 
   await popPrefs();
 });
 
-function dropText(text, expectedTabOpenCount = 0) {
-  return drop([[{type: "text/plain", data: text}]], expectedTabOpenCount);
+function dropText(text, expectedURLs) {
+  return drop([[{type: "text/plain", data: text}]], expectedURLs);
 }
 
-async function drop(dragData, expectedTabOpenCount = 0) {
+async function drop(dragData, expectedURLs) {
   let dragDataString = JSON.stringify(dragData);
-  info(`Starting test for datagData:${dragDataString}; expectedTabOpenCount:${expectedTabOpenCount}`);
+  info(`Starting test for dragData:${dragDataString}; expectedURLs.length:${expectedURLs.length}`);
   let EventUtils = {};
   Services.scriptloader.loadSubScript("chrome://mochikit/content/tests/SimpleTest/EventUtils.js", EventUtils);
 
   let awaitDrop = BrowserTestUtils.waitForEvent(gBrowser.tabContainer, "drop");
-  let actualTabOpenCount = 0;
-  let openedTabs = [];
-  let checkCount = function(event) {
-    openedTabs.push(event.target);
-    actualTabOpenCount++;
-    return actualTabOpenCount == expectedTabOpenCount;
-  };
-  let awaitTabOpen = expectedTabOpenCount && BrowserTestUtils.waitForEvent(gBrowser.tabContainer, "TabOpen", false, checkCount);
+
+  let loadedPromises = expectedURLs.map(
+    url => BrowserTestUtils.waitForNewTab(gBrowser, url, false, true));
+
   // A drop type of "link" onto an existing tab would normally trigger a
   // load in that same tab, but tabbrowser code in _getDragTargetTab treats
   // drops on the outer edges of a tab differently (loading a new tab
   // instead). Make events created by synthesizeDrop have all of their
   // coordinates set to 0 (screenX/screenY), so they're treated as drops
   // on the outer edge of the tab, thus they open new tabs.
   var event = {
     clientX: 0,
     clientY: 0,
     screenX: 0,
     screenY: 0,
   };
   EventUtils.synthesizeDrop(gBrowser.selectedTab, gBrowser.selectedTab, dragData, "link", window, undefined, event);
-  let tabsOpened = false;
-  if (awaitTabOpen) {
-    await awaitTabOpen;
-    info("Got TabOpen event");
-    tabsOpened = true;
-    for (let tab of openedTabs) {
-      BrowserTestUtils.removeTab(tab);
-    }
+
+  let tabs = await Promise.all(loadedPromises);
+  for (let tab of tabs) {
+    BrowserTestUtils.removeTab(tab);
   }
-  is(tabsOpened, !!expectedTabOpenCount, `Tabs for ${dragDataString} should only open if any of dropped items are valid`);
 
   await awaitDrop;
   ok(true, "Got drop event");
 }

--- a/browser/base/content/test/popups/browser_popupUI.js
+++ b/browser/base/content/test/popups/browser_popupUI.js
@@ -1,13 +1,13 @@
 function test() {
   waitForExplicitFinish();
   SpecialPowers.pushPrefEnv({ set: [[ "dom.disable_open_during_load", false ]] });
 
-  let popupOpened = BrowserTestUtils.waitForNewWindow("about:blank");
+  let popupOpened = BrowserTestUtils.waitForNewWindow({url: "about:blank"});
   BrowserTestUtils.openNewForegroundTab(gBrowser,
     "data:text/html,<html><script>popup=open('about:blank','','width=300,height=200')</script>"
   );
   popupOpened.then((win) => testPopupUI(win));
 }
 
 function testPopupUI(win) {
   var doc = win.document;

--- a/browser/components/extensions/parent/ext-browser.js
+++ b/browser/components/extensions/parent/ext-browser.js
@@ -26,17 +26,17 @@ let windowTracker;
 const getSender = (extension, target, sender) => {
   let tabId;
   if ("tabId" in sender) {
     // The message came from a privileged extension page running in a tab. In
     // that case, it should include a tabId property (which is filled in by the
     // page-open listener below).
     tabId = sender.tabId;
     delete sender.tabId;
-  } else if (target instanceof Ci.nsIDOMXULElement ||
+  } else if (ExtensionUtils.instanceOf(target, "XULElement") ||
              ExtensionUtils.instanceOf(target, "HTMLIFrameElement")) {
     tabId = tabTracker.getBrowserData(target).tabId;
   }
 
   if (tabId) {
     let tab = extension.tabManager.get(tabId, null);
     if (tab) {
       sender.tab = tab.convert();

--- a/browser/components/extensions/test/browser/browser_ext_windows.js
+++ b/browser/components/extensions/test/browser/browser_ext_windows.js
@@ -89,17 +89,17 @@ add_task(async function testWindowTitle(
       permissions: ["tabs"],
     },
   });
 
   await extension.startup();
   let {Management: {global: {windowTracker}}} = ChromeUtils.import("resource://gre/modules/Extension.jsm", {});
 
   async function createApiWin(options) {
-    let promiseLoaded = BrowserTestUtils.waitForNewWindow(START_URL);
+    let promiseLoaded = BrowserTestUtils.waitForNewWindow({url: START_URL});
     extension.sendMessage("create", options);
     let apiWin = await extension.awaitMessage("created");
     let realWin = windowTracker.getWindow(apiWin.id);
     await promiseLoaded;
     let expectedPreface = options.titlePreface ? options.titlePreface : "";
     ok(realWin.document.title.startsWith(expectedPreface),
        "Created window has the expected title preface.");
     ok(realWin.document.title.includes(START_TITLE),

--- a/browser/components/privatebrowsing/test/browser/browser_oa_private_browsing_window.js
+++ b/browser/components/privatebrowsing/test/browser/browser_oa_private_browsing_window.js
@@ -1,17 +1,17 @@
 "use strict";
 
 const PATH = getRootDirectory(gTestPath).replace("chrome://mochitests/content", "http://example.com");
 const TEST_PAGE = PATH + "file_triggeringprincipal_oa.html";
 const DUMMY_PAGE = PATH + "empty_file.html";
 
 add_task(async function test_principal_right_click_open_link_in_new_private_win() {
   await BrowserTestUtils.withNewTab(TEST_PAGE, async function(browser) {
-    let promiseNewWindow = BrowserTestUtils.waitForNewWindow(DUMMY_PAGE);
+    let promiseNewWindow = BrowserTestUtils.waitForNewWindow({url: DUMMY_PAGE});
 
     // simulate right-click open link in new private window
     BrowserTestUtils.waitForEvent(document, "popupshown", false, event => {
       document.getElementById("context-openlinkprivate").doCommand();
       event.target.hidePopup();
       return true;
     });
     BrowserTestUtils.synthesizeMouseAtCenter("#checkPrincipalOA",

--- a/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_newtab_from_popup.js
+++ b/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_newtab_from_popup.js
@@ -35,17 +35,17 @@ add_task(async function test_private_pop
   // First, open a private browsing window, and load our
   // testing page.
   let privBrowser = privWin.gBrowser.selectedBrowser;
   await BrowserTestUtils.loadURI(privBrowser, WINDOW_BODY);
   await BrowserTestUtils.browserLoaded(privBrowser);
 
   // Next, click on the link in the testing page, and ensure
   // that a private popup window is opened.
-  let openedPromise = BrowserTestUtils.waitForNewWindow(POPUP_LINK);
+  let openedPromise = BrowserTestUtils.waitForNewWindow({url: POPUP_LINK});
 
   await BrowserTestUtils.synthesizeMouseAtCenter("#first", {}, privBrowser);
   let popupWin = await openedPromise;
   ok(PrivateBrowsingUtils.isWindowPrivate(popupWin),
      "Popup window was private.");
 
   // Now click on the link in the popup, and ensure that a new
   // tab is opened in the original private browsing window.

--- a/browser/components/sessionstore/test/browser_394759_behavior.js
+++ b/browser/components/sessionstore/test/browser_394759_behavior.js
@@ -21,17 +21,17 @@
  */
 function testWindows(windowsToOpen, expectedResults) {
   return (async function() {
     for (let winData of windowsToOpen) {
       let features = "chrome,dialog=no," +
                      (winData.isPopup ? "all=no" : "all");
       let url = "http://example.com/?window=" + windowsToOpen.length;
 
-      let openWindowPromise = BrowserTestUtils.waitForNewWindow(url);
+      let openWindowPromise = BrowserTestUtils.waitForNewWindow({url});
       openDialog(getBrowserURL(), "", features, url);
       let win = await openWindowPromise;
       await BrowserTestUtils.closeWindow(win);
     }
 
     let closedWindowData = JSON.parse(ss.getClosedWindowData());
     let numPopups = closedWindowData.filter(function(el, i, arr) {
       return el.isPopup;

new file mode 100644
--- /dev/null
+++ b/dom/base/crashtests/1449601.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html>
+  <body>
+    <script>
+      var blob = new Blob(["foo"], { type: "text/plain" });
+      var url = URL.createObjectURL(blob);
+      var ifr = document.createElement("iframe");
+      ifr.src = url;
+      document.body.appendChild(ifr);
+
+      onload = function() {
+        try { window.find('foo',false,true,true,true,true) } catch(e) { }
+      }
+    </script>
+  </body>
+</html>

--- a/dom/base/crashtests/crashtests.list
+++ b/dom/base/crashtests/crashtests.list
@@ -233,9 +233,10 @@ load 1405771.html
 load 1406109-1.html
 pref(dom.webcomponents.shadowdom.enabled,true) load 1324463.html
 pref(dom.webcomponents.customelements.enabled,true) load 1413815.html
 load 1411473.html
 pref(dom.webcomponents.shadowdom.enabled,false) load 1422931.html
 pref(dom.webcomponents.shadowdom.enabled,true) load 1419799.html
 skip-if(!browserIsRemote) pref(dom.webcomponents.customelements.enabled,true) pref(dom.disable_open_during_load,false) load 1419902.html # skip on non e10s loads, Bug 1419902
 pref(dom.webcomponents.shadowdom.enabled,true) load 1428053.html
+load 1449601.html
 load 1445670.html

--- a/dom/base/moz.build
+++ b/dom/base/moz.build
@@ -13,17 +13,16 @@ with Files("**"):
 TEST_DIRS += ['test']
 
 XPIDL_SOURCES += [
     'mozIDOMWindow.idl',
     'nsIContentPolicy.idl',
     'nsIDocumentEncoder.idl',
     'nsIDOMDOMRequest.idl',
     'nsIDOMParser.idl',
-    'nsIDOMSerializer.idl',
     'nsIDroppedLinkHandler.idl',
     'nsIFrameLoaderOwner.idl',
     'nsIImageLoadingContent.idl',
     'nsIMessageManager.idl',
     'nsIObjectLoadingContent.idl',
     'nsIPerformanceMetrics.idl',
     'nsIRemoteWindowContext.idl',
     'nsIScriptChannel.idl',

--- a/dom/base/nsDOMSerializer.cpp
+++ b/dom/base/nsDOMSerializer.cpp
@@ -17,130 +17,106 @@
 #include "nsINode.h"
 
 using namespace mozilla;
 
 nsDOMSerializer::nsDOMSerializer()
 {
 }
 
-nsDOMSerializer::~nsDOMSerializer()
+static already_AddRefed<nsIDocumentEncoder>
+SetUpEncoder(nsINode& aRoot, const nsAString& aCharset, ErrorResult& aRv)
 {
-}
-
-// QueryInterface implementation for nsDOMSerializer
-NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsDOMSerializer)
-  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
-  NS_INTERFACE_MAP_ENTRY(nsISupports)
-  NS_INTERFACE_MAP_ENTRY(nsIDOMSerializer)
-NS_INTERFACE_MAP_END
-
-NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(nsDOMSerializer, mOwner)
-
-NS_IMPL_CYCLE_COLLECTING_ADDREF(nsDOMSerializer)
-NS_IMPL_CYCLE_COLLECTING_RELEASE(nsDOMSerializer)
-
-
-static nsresult
-SetUpEncoder(nsIDOMNode *aRoot, const nsACString& aCharset,
-             nsIDocumentEncoder **aEncoder)
-{
-  *aEncoder = nullptr;
-
   nsresult rv;
   nsCOMPtr<nsIDocumentEncoder> encoder =
     do_CreateInstance(NS_DOC_ENCODER_CONTRACTID_BASE "application/xhtml+xml", &rv);
-  if (NS_FAILED(rv))
-    return rv;
+  if (NS_FAILED(rv)) {
+    aRv.Throw(rv);
+    return nullptr;
+  }
 
-  nsCOMPtr<nsINode> root = do_QueryInterface(aRoot);
-  MOZ_ASSERT(root);
-
-  nsIDocument* doc = root->OwnerDoc();
-  bool entireDocument = (doc == root);
-  nsCOMPtr<nsIDOMDocument> domDoc(do_QueryInterface(doc));
+  nsIDocument* doc = aRoot.OwnerDoc();
+  bool entireDocument = (doc == &aRoot);
 
   // This method will fail if no document
-  rv = encoder->Init(domDoc, NS_LITERAL_STRING("application/xhtml+xml"),
-                     nsIDocumentEncoder::OutputRaw |
-                     nsIDocumentEncoder::OutputDontRewriteEncodingDeclaration);
+  rv = encoder->
+    NativeInit(doc, NS_LITERAL_STRING("application/xhtml+xml"),
+               nsIDocumentEncoder::OutputRaw |
+               nsIDocumentEncoder::OutputDontRewriteEncodingDeclaration);
 
-  if (NS_FAILED(rv))
-    return rv;
+  if (NS_FAILED(rv)) {
+    aRv.Throw(rv);
+    return nullptr;
+  }
 
-  nsAutoCString charset(aCharset);
+  NS_ConvertUTF16toUTF8 charset(aCharset);
   if (charset.IsEmpty()) {
-    nsCOMPtr<nsIDocument> doc = do_QueryInterface(domDoc);
-    NS_ASSERTION(doc, "Need a document");
     doc->GetDocumentCharacterSet()->Name(charset);
   }
   rv = encoder->SetCharset(charset);
-  if (NS_FAILED(rv))
-    return rv;
+  if (NS_FAILED(rv)) {
+    aRv.Throw(rv);
+    return nullptr;
+  }
 
   // If we are working on the entire document we do not need to
   // specify which part to serialize
   if (!entireDocument) {
-    rv = encoder->SetNode(aRoot);
+    rv = encoder->SetNativeNode(&aRoot);
   }
 
-  if (NS_SUCCEEDED(rv)) {
-    encoder.forget(aEncoder);
+  if (NS_FAILED(rv)) {
+    aRv.Throw(rv);
+    return nullptr;
   }
 
-  return rv;
+  return encoder.forget();
 }
 
 void
 nsDOMSerializer::SerializeToString(nsINode& aRoot, nsAString& aStr,
-                                   ErrorResult& rv)
+                                   ErrorResult& aRv)
 {
-  rv = nsDOMSerializer::SerializeToString(aRoot.AsDOMNode(), aStr);
-}
+  aStr.Truncate();
 
-NS_IMETHODIMP
-nsDOMSerializer::SerializeToString(nsIDOMNode *aRoot, nsAString& _retval)
-{
-  NS_ENSURE_ARG_POINTER(aRoot);
-
-  _retval.Truncate();
-
-  if (!nsContentUtils::CanCallerAccess(aRoot)) {
-    return NS_ERROR_DOM_SECURITY_ERR;
+  if (!nsContentUtils::CanCallerAccess(&aRoot)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
   }
 
-  nsCOMPtr<nsIDocumentEncoder> encoder;
-  nsresult rv = SetUpEncoder(aRoot, EmptyCString(), getter_AddRefs(encoder));
-  if (NS_FAILED(rv))
-    return rv;
+  nsCOMPtr<nsIDocumentEncoder> encoder =
+    SetUpEncoder(aRoot, EmptyString(), aRv);
+  if (aRv.Failed()) {
+    return;
+  }
 
-  return encoder->EncodeToString(_retval);
+  nsresult rv = encoder->EncodeToString(aStr);
+  if (NS_FAILED(rv)) {
+    aRv.Throw(rv);
+  }
 }
 
 void
 nsDOMSerializer::SerializeToStream(nsINode& aRoot, nsIOutputStream* aStream,
-                                   const nsAString& aCharset, ErrorResult& rv)
+                                   const nsAString& aCharset,
+                                   ErrorResult& aRv)
 {
-  rv = nsDOMSerializer::SerializeToStream(aRoot.AsDOMNode(), aStream,
-                                          NS_ConvertUTF16toUTF8(aCharset));
-}
+  if (NS_WARN_IF(!aStream)) {
+    aRv.Throw(NS_ERROR_INVALID_ARG);
+    return;
+  }
 
-NS_IMETHODIMP
-nsDOMSerializer::SerializeToStream(nsIDOMNode *aRoot,
-                                   nsIOutputStream *aStream,
-                                   const nsACString& aCharset)
-{
-  NS_ENSURE_ARG_POINTER(aRoot);
-  NS_ENSURE_ARG_POINTER(aStream);
   // The charset arg can be empty, in which case we get the document's
   // charset and use that when serializing.
 
-  if (!nsContentUtils::CanCallerAccess(aRoot)) {
-    return NS_ERROR_DOM_SECURITY_ERR;
+  // No point doing a CanCallerAccess check, because we can only be
+  // called by system JS or C++.
+  nsCOMPtr<nsIDocumentEncoder> encoder =
+    SetUpEncoder(aRoot, aCharset, aRv);
+  if (aRv.Failed()) {
+    return;
   }
 
-  nsCOMPtr<nsIDocumentEncoder> encoder;
-  nsresult rv = SetUpEncoder(aRoot, aCharset, getter_AddRefs(encoder));
-  if (NS_FAILED(rv))
-    return rv;
-
-  return encoder->EncodeToStream(aStream);
+  nsresult rv = encoder->EncodeToStream(aStream);
+  if (NS_FAILED(rv)) {
+    aRv.Throw(rv);
+  }
 }

--- a/dom/base/nsDOMSerializer.h
+++ b/dom/base/nsDOMSerializer.h
@@ -2,68 +2,48 @@
 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
 
 #ifndef nsDOMSerializer_h_
 #define nsDOMSerializer_h_
 
-#include "nsIDOMSerializer.h"
-#include "nsWrapperCache.h"
+#include "mozilla/dom/NonRefcountedDOMObject.h"
 #include "mozilla/ErrorResult.h"
 #include "mozilla/dom/XMLSerializerBinding.h"
 
 class nsINode;
+class nsIOutputStream;
 
-class nsDOMSerializer final : public nsIDOMSerializer,
-                              public nsWrapperCache
+class nsDOMSerializer final : public mozilla::dom::NonRefcountedDOMObject
 {
 public:
   nsDOMSerializer();
 
-  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
-  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(nsDOMSerializer)
-
-  // nsIDOMSerializer
-  NS_DECL_NSIDOMSERIALIZER
-
   // WebIDL API
-  static already_AddRefed<nsDOMSerializer>
+  static nsDOMSerializer*
   Constructor(const mozilla::dom::GlobalObject& aOwner,
               mozilla::ErrorResult& rv)
   {
-    RefPtr<nsDOMSerializer> domSerializer = new nsDOMSerializer(aOwner.GetAsSupports());
-    return domSerializer.forget();
+    return new nsDOMSerializer();
   }
 
   void
   SerializeToString(nsINode& aRoot, nsAString& aStr,
                     mozilla::ErrorResult& rv);
 
   void
   SerializeToStream(nsINode& aRoot, nsIOutputStream* aStream,
-                    const nsAString& aCharset, mozilla::ErrorResult& rv);
+                    const nsAString& aCharset,
+                    mozilla::ErrorResult& aRv);
 
-  nsISupports* GetParentObject() const
+  bool WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto,
+                  JS::MutableHandle<JSObject*> aReflector)
   {
-    return mOwner;
-  }
-
-  virtual JSObject* WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override
-  {
-    return mozilla::dom::XMLSerializerBinding::Wrap(aCx, this, aGivenProto);
+    return mozilla::dom::XMLSerializerBinding::Wrap(aCx, this, aGivenProto,
+                                                    aReflector);
   }
-
-private:
-  virtual ~nsDOMSerializer();
-
-  explicit nsDOMSerializer(nsISupports* aOwner) : mOwner(aOwner)
-  {
-    MOZ_ASSERT(aOwner);
-  }
-
-  nsCOMPtr<nsISupports> mOwner;
 };
 
 
 #endif
 

--- a/dom/base/nsFrameLoader.cpp
+++ b/dom/base/nsFrameLoader.cpp
@@ -152,18 +152,18 @@ NS_IMPL_CYCLE_COLLECTING_RELEASE(nsFrame
 
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsFrameLoader)
   NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
   if (aIID.Equals(NS_GET_IID(nsFrameLoader))) {
       // We want to end up with a pointer that can then be reinterpret_cast
       // from nsISupports* to nsFrameLoader* and end up with |this|.
       foundInterface = reinterpret_cast<nsISupports*>(this);
   } else
-  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIWebBrowserPersistable)
-  NS_INTERFACE_MAP_ENTRY(nsIWebBrowserPersistable)
+  NS_INTERFACE_MAP_ENTRY(nsIMutationObserver)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
 NS_INTERFACE_MAP_END
 
 nsFrameLoader::nsFrameLoader(Element* aOwner, nsPIDOMWindowOuter* aOpener,
                              bool aNetworkCreated, int32_t aJSPluginID)
   : mOwnerContent(aOwner)
   , mDetachedSubdocFrame(nullptr)
   , mOpener(aOpener)
   , mRemoteBrowser(nullptr)
@@ -3225,32 +3225,21 @@ nsFrameLoader::DestroyBrowserFrameScript
   }
 }
 
 void
 nsFrameLoader::StartPersistence(uint64_t aOuterWindowID,
                                 nsIWebBrowserPersistDocumentReceiver* aRecv,
                                 ErrorResult& aRv)
 {
-  nsresult rv = StartPersistence(aOuterWindowID, aRecv);
-  if (NS_FAILED(rv)) {
-    aRv.Throw(rv);
-  }
-}
-
-NS_IMETHODIMP
-nsFrameLoader::StartPersistence(uint64_t aOuterWindowID,
-                                nsIWebBrowserPersistDocumentReceiver* aRecv)
-{
-  if (!aRecv) {
-    return NS_ERROR_INVALID_POINTER;
-  }
+  MOZ_ASSERT(aRecv);
 
   if (mRemoteBrowser) {
-    return mRemoteBrowser->StartPersistence(aOuterWindowID, aRecv);
+    mRemoteBrowser->StartPersistence(aOuterWindowID, aRecv, aRv);
+    return;
   }
 
   nsCOMPtr<nsIDocument> rootDoc =
     mDocShell ? mDocShell->GetDocument() : nullptr;
   nsCOMPtr<nsIDocument> foundDoc;
   if (aOuterWindowID) {
     foundDoc = nsContentUtils::GetSubdocumentWithOuterWindowId(rootDoc, aOuterWindowID);
   } else {
@@ -3259,17 +3248,16 @@ nsFrameLoader::StartPersistence(uint64_t
 
   if (!foundDoc) {
     aRecv->OnError(NS_ERROR_NO_CONTENT);
   } else {
     nsCOMPtr<nsIWebBrowserPersistDocument> pdoc =
       new mozilla::WebBrowserPersistLocalDocument(foundDoc);
     aRecv->OnDocumentReady(pdoc);
   }
-  return NS_OK;
 }
 
 void
 nsFrameLoader::MaybeUpdatePrimaryTabParent(TabParentChange aChange)
 {
   if (mRemoteBrowser && mOwnerContent) {
     nsCOMPtr<nsIDocShell> docShell = mOwnerContent->OwnerDoc()->GetDocShell();
     if (!docShell) {

--- a/dom/base/nsFrameLoader.h
+++ b/dom/base/nsFrameLoader.h
@@ -20,32 +20,32 @@
 #include "nsWrapperCache.h"
 #include "nsIURI.h"
 #include "nsFrameMessageManager.h"
 #include "mozilla/dom/BindingUtils.h"
 #include "mozilla/dom/Element.h"
 #include "mozilla/Attributes.h"
 #include "nsStubMutationObserver.h"
 #include "Units.h"
-#include "nsIWebBrowserPersistable.h"
 #include "nsIFrame.h"
 #include "nsPluginTags.h"
 
 class nsIURI;
 class nsSubDocumentFrame;
 class nsView;
 class nsInProcessTabChildGlobal;
 class AutoResetInShow;
 class AutoResetInFrameSwap;
 class nsITabParent;
 class nsIDocShellTreeItem;
 class nsIDocShellTreeOwner;
 class nsILoadContext;
 class nsIMessageSender;
 class nsIPrintSettings;
+class nsIWebBrowserPersistDocumentReceiver;
 class nsIWebProgressListener;
 
 namespace mozilla {
 
 class OriginAttributes;
 
 namespace dom {
 class ChromeMessageSender;
@@ -71,18 +71,17 @@ class RenderFrameParent;
 typedef struct _GtkWidget GtkWidget;
 #endif
 
 // IID for nsFrameLoader, because some places want to QI to it.
 #define NS_FRAMELOADER_IID                                      \
   { 0x297fd0ea, 0x1b4a, 0x4c9a,                                 \
       { 0xa4, 0x04, 0xe5, 0x8b, 0xe8, 0x95, 0x10, 0x50 } }
 
-class nsFrameLoader final : public nsIWebBrowserPersistable,
-                            public nsStubMutationObserver,
+class nsFrameLoader final : public nsStubMutationObserver,
                             public mozilla::dom::ipc::MessageManagerCallback,
                             public nsWrapperCache
 {
   friend class AutoResetInShow;
   friend class AutoResetInFrameSwap;
   typedef mozilla::dom::PBrowserParent PBrowserParent;
   typedef mozilla::dom::TabParent TabParent;
   typedef mozilla::layout::RenderFrameParent RenderFrameParent;
@@ -91,20 +90,19 @@ public:
   static nsFrameLoader* Create(mozilla::dom::Element* aOwner,
                                nsPIDOMWindowOuter* aOpener,
                                bool aNetworkCreated,
                                int32_t aJSPluginID = nsFakePluginTag::NOT_JSPLUGIN);
 
   NS_DECLARE_STATIC_IID_ACCESSOR(NS_FRAMELOADER_IID)
 
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
-  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(nsFrameLoader,
-                                                         nsIWebBrowserPersistable)
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(nsFrameLoader)
+
   NS_DECL_NSIMUTATIONOBSERVER_ATTRIBUTECHANGED
-  NS_DECL_NSIWEBBROWSERPERSISTABLE
   nsresult CheckForRecursiveLoad(nsIURI* aURI);
   nsresult ReallyStartLoading();
   void StartDestroy();
   void DestroyDocShell();
   void DestroyComplete();
   nsIDocShell* GetExistingDocShell() { return mDocShell; }
   mozilla::dom::EventTarget* GetTabChildGlobalAsEventTarget();
   nsresult CreateStaticClone(nsFrameLoader* aDest);
@@ -506,12 +504,12 @@ private:
   bool mFreshProcess : 1;
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(nsFrameLoader, NS_FRAMELOADER_IID)
 
 inline nsISupports*
 ToSupports(nsFrameLoader* aFrameLoader)
 {
-  return static_cast<nsIWebBrowserPersistable*>(aFrameLoader);
+  return aFrameLoader;
 }
 
 #endif

deleted file mode 100644
--- a/dom/base/nsIDOMSerializer.idl
+++ /dev/null
@@ -1,53 +0,0 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* 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 "nsISupports.idl"
-
-interface nsIOutputStream;
-interface nsIDOMNode;
-
-/**
- * The nsIDOMSerializer interface is really a placeholder till the W3C
- * DOM Working Group defines a mechanism for serializing DOM nodes.
- * An instance of this interface can be used to serialize a DOM document
- * or any DOM subtree.
- */
-
-[uuid(9fd4ba15-e67c-4c98-b52c-7715f62c9196)]
-interface nsIDOMSerializer : nsISupports
-{
-  /**
-   * The subtree rooted by the specified element is serialized to
-   * a string.
-   * 
-   * @param root The root of the subtree to be serialized. This could
-   *             be any node, including a Document.
-   * @returns The serialized subtree in the form of a Unicode string
-   */
-  AString serializeToString(in nsIDOMNode root);
-
-  /**
-   * The subtree rooted by the specified element is serialized to
-   * a byte stream using the character set specified.
-   * @param root The root of the subtree to be serialized. This could
-   *             be any node, including a Document.
-   * @param stream The byte stream to which the subtree is serialized.
-   * @param charset The name of the character set to use for the encoding
-   *                to a byte stream.  If this string is empty and root is
-   *                a document, the document's character set will be used.
-   */
-  void serializeToStream(in nsIDOMNode root, in nsIOutputStream stream,
-                         in AUTF8String charset);
-};
-
-%{ C++
-#define NS_XMLSERIALIZER_CID                        \
- { /* a6cf9124-15b3-11d2-932e-00805f8add32 */       \
-   0xa6cf9124, 0x15b3, 0x11d2,                      \
-  {0x93, 0x2e, 0x00, 0x80, 0x5f, 0x8a, 0xdd, 0x32} }
-#define NS_XMLSERIALIZER_CONTRACTID \
-"@mozilla.org/xmlextras/xmlserializer;1"
-%}
-

--- a/dom/base/test/chrome/test_domparsing.xul
+++ b/dom/base/test/chrome/test_domparsing.xul
@@ -65,18 +65,17 @@ runTest(new DOMParser(), new XMLSerializ
   parser.init();
   throws(function() {
     parser.init();
   }, "NS_ERROR_UNEXPECTED", "init method should throw when called twice");
 }
 
 runTest(Cc["@mozilla.org/xmlextras/domparser;1"]
         .createInstance(Ci.nsIDOMParser),
-        Cc["@mozilla.org/xmlextras/xmlserializer;1"]
-        .createInstance(Ci.nsIDOMSerializer));
+        new XMLSerializer());
 
 function runTest(parser, serializer) {
   is(typeof parser.parseFromString, "function", "parseFromString should exist");
   is(typeof parser.parseFromBuffer, "function", "parseFromBuffer should exist");
   is(typeof parser.parseFromStream, "function", "parseFromStream should exist");
   is(typeof parser.init, "function", "init should exist");
 
   is(typeof serializer.serializeToString, "function", "serializeToString should exist");

--- a/dom/base/test/unit/head_xml.js
+++ b/dom/base/test/unit/head_xml.js
@@ -8,22 +8,22 @@ const I                    = Ci;
 const C                    = Cc;
 
 const nsIFile         = I.nsIFile;
 const nsIProperties        = I.nsIProperties;
 const nsIFileInputStream   = I.nsIFileInputStream;
 const nsIInputStream       = I.nsIInputStream;
 
 const nsIDOMParser         = I.nsIDOMParser;
-const nsIDOMSerializer     = I.nsIDOMSerializer;
 const nsIDOMDocument       = I.nsIDOMDocument;
 const nsIDOMElement        = I.nsIDOMElement;
 const nsIDOMNode           = I.nsIDOMNode;
 const nsIDOMNodeList       = I.nsIDOMNodeList;
-const nsIDOMXULElement     = I.nsIDOMXULElement;
+
+Cu.importGlobalProperties(["XMLSerializer"]);
 
 function DOMParser() {
   var parser = C["@mozilla.org/xmlextras/domparser;1"].createInstance(nsIDOMParser);
   parser.init();
   return parser;
 }
 
 var __testsDirectory = null;
@@ -54,18 +54,17 @@ function ParseXML(data) {
 
   Assert.equal(data instanceof nsIInputStream, true);
   
   return DOMParser().parseFromStream(data, "UTF-8", data.available(),
                                      "application/xml");
 }
 
 function DOMSerializer() {
-  return C["@mozilla.org/xmlextras/xmlserializer;1"]
-          .createInstance(nsIDOMSerializer);
+  return new XMLSerializer();
 }
 
 function SerializeXML(node) {
   return DOMSerializer().serializeToString(node);
 }
 
 function roundtrip(obj) {
   if (typeof(obj) == "string") {

--- a/dom/base/test/unit/test_nodelist.js
+++ b/dom/base/test/unit/test_nodelist.js
@@ -170,30 +170,30 @@ function test_getElementsByTagNameNS()
 function test_getElementsByAttribute()
 {
   var doc = ParseFile("nodelist_data_2.xul");
   var root = doc.documentElement;
 
   // Sadly, DOMParser can't create XULDocument objects.  But at least we have a
   // XULElement!
 
-  Assert.ok(root instanceof nsIDOMXULElement);
+  Assert.equal(ChromeUtils.getClassName(root), "XULElement");
 
   Assert.ok(root.getElementsByAttribute("foo", "foo") instanceof
             nsIDOMNodeList);
 
   var master1 = doc.getElementById("master1");
   var master2 = doc.getElementById("master2");
   var master3 = doc.getElementById("master3");
   var external = doc.getElementById("external");
 
-  Assert.ok(master1 instanceof nsIDOMXULElement);
-  Assert.ok(master2 instanceof nsIDOMXULElement);
-  Assert.ok(master3 instanceof nsIDOMXULElement);
-  Assert.ok(external instanceof nsIDOMXULElement);
+  Assert.equal(ChromeUtils.getClassName(master1), "XULElement");
+  Assert.equal(ChromeUtils.getClassName(master2), "XULElement");
+  Assert.equal(ChromeUtils.getClassName(master3), "XULElement");
+  Assert.equal(ChromeUtils.getClassName(external), "XULElement");
 
   // Basic tests
   Assert.equal(root.getElementsByAttribute("foo", "foo").length,
                14);
   Assert.equal(master1.getElementsByAttribute("foo", "foo").length,
                4);
 
   Assert.equal(root.getElementsByAttribute("foo", "bar").length,
@@ -287,31 +287,31 @@ function test_getElementsByAttribute()
 function test_getElementsByAttributeNS()
 {
   var doc = ParseFile("nodelist_data_2.xul");
   var root = doc.documentElement;
 
   // Sadly, DOMParser can't create XULDocument objects.  But at least we have a
   // XULElement!
 
-  Assert.ok(root instanceof nsIDOMXULElement);
+  Assert.equal(ChromeUtils.getClassName(root), "XULElement");
 
   // Check that getElementsByAttributeNS returns a nodelist.
   Assert.ok(root.getElementsByAttributeNS("*", "*", "*") instanceof
             nsIDOMNodeList);
 
   var master1 = doc.getElementById("master1");
   var master2 = doc.getElementById("master2");
   var master3 = doc.getElementById("master3");
   var external = doc.getElementById("external");
 
-  Assert.ok(master1 instanceof nsIDOMXULElement);
-  Assert.ok(master2 instanceof nsIDOMXULElement);
-  Assert.ok(master3 instanceof nsIDOMXULElement);
-  Assert.ok(external instanceof nsIDOMXULElement);
+  Assert.equal(ChromeUtils.getClassName(master1), "XULElement");
+  Assert.equal(ChromeUtils.getClassName(master2), "XULElement");
+  Assert.equal(ChromeUtils.getClassName(master3), "XULElement");
+  Assert.equal(ChromeUtils.getClassName(external), "XULElement");
   
   // Test wildcard namespace
   Assert.equal(root.getElementsByAttributeNS("*", "foo", "foo").length,
                38);
   Assert.equal(master1.getElementsByAttributeNS("*", "foo", "foo").length,
                11);
   Assert.equal(master2.getElementsByAttributeNS("*", "foo", "foo").length,
                10);

--- a/dom/bindings/Bindings.conf
+++ b/dom/bindings/Bindings.conf
@@ -1381,16 +1381,17 @@ DOMInterfaces = {
 },
 
 'XMLHttpRequestEventTarget': {
     'concrete': False
 },
 
 'XMLSerializer': {
     'nativeType': 'nsDOMSerializer',
+    'wrapperCache': False
 },
 
 'XPathEvaluator': {
     'wrapperCache': False
 },
 
 'XPathExpression': {
     'wrapperCache': False,

--- a/dom/events/EventDispatcher.cpp
+++ b/dom/events/EventDispatcher.cpp
@@ -744,20 +744,39 @@ EventDispatcher::Dispatch(nsISupports* a
     }
   }
 
 #ifdef DEBUG
   if (NS_IsMainThread() &&
       aEvent->mMessage != eVoidEvent &&
       !nsContentUtils::IsSafeToRunScript()) {
     nsCOMPtr<nsINode> node = do_QueryInterface(target);
-    if (node && nsContentUtils::IsChromeDoc(node->OwnerDoc())) {
-      NS_WARNING("Fix the caller!");
+    if (!node) {
+      // If the target is not a node, just go ahead and assert that this is
+      // unsafe.  There really shouldn't be any other event targets in documents
+      // that are not being rendered or scripted.
+      NS_ERROR("This is unsafe! Fix the caller!");
     } else {
-      NS_ERROR("This is unsafe! Fix the caller!");
+      // If this is a node, it's possible that this is some sort of DOM tree
+      // that is never accessed by script (for example an SVG image or XBL
+      // binding document or whatnot).  We really only want to warn/assert here
+      // if there might be actual scripted listeners for this event, so restrict
+      // the warnings/asserts to the case when script can or once could touch
+      // this node's document.
+      nsIDocument* doc = node->OwnerDoc();
+      bool hasHadScriptHandlingObject;
+      nsIGlobalObject* global =
+        doc->GetScriptHandlingObject(hasHadScriptHandlingObject);
+      if (global || hasHadScriptHandlingObject) {
+        if (nsContentUtils::IsChromeDoc(doc)) {
+          NS_WARNING("Fix the caller!");
+        } else {
+          NS_ERROR("This is unsafe! Fix the caller!");
+        }
+      }
     }
   }
 
   if (aDOMEvent) {
     WidgetEvent* innerEvent = aDOMEvent->WidgetEventPtr();
     NS_ASSERTION(innerEvent == aEvent,
                   "The inner event of aDOMEvent is not the same as aEvent!");
   }

--- a/dom/events/EventListenerManager.cpp
+++ b/dom/events/EventListenerManager.cpp
@@ -681,33 +681,49 @@ EventListenerManager::ListenerCanHandle(
     if (!aEvent->mFlags.mInSystemGroup && !aListener->mIsChrome) {
       return false;
     }
   }
   MOZ_ASSERT(mIsMainThreadELM);
   return aListener->mEventMessage == aEventMessage;
 }
 
+static bool
+DefaultToPassiveTouchListeners()
+{
+  static bool sDefaultToPassiveTouchListeners = false;
+  static bool sIsPrefCached = false;
+
+  if (!sIsPrefCached) {
+    sIsPrefCached = true;
+    Preferences::AddBoolVarCache(&sDefaultToPassiveTouchListeners,
+                                 "dom.event.default_to_passive_touch_listeners");
+  }
+
+  return sDefaultToPassiveTouchListeners;
+}
+
 void
 EventListenerManager::AddEventListenerByType(
                         EventListenerHolder aListenerHolder,
                         const nsAString& aType,
                         const EventListenerFlags& aFlags,
                         const Optional<bool>& aPassive)
 {
   RefPtr<nsAtom> atom;
   EventMessage message = mIsMainThreadELM ?
     nsContentUtils::GetEventMessageAndAtomForListener(aType,
                                                       getter_AddRefs(atom)) :
     eUnidentifiedEvent;
 
   EventListenerFlags flags = aFlags;
   if (aPassive.WasPassed()) {
     flags.mPassive = aPassive.Value();
-  } else if (message == eTouchStart || message == eTouchMove) {
+  } else if ((message == eTouchStart || message == eTouchMove) &&
+             mIsMainThreadELM && DefaultToPassiveTouchListeners()) {
     nsCOMPtr<nsINode> node;
     nsCOMPtr<nsPIDOMWindowInner> win;
     if ((win = GetTargetAsInnerWindow()) ||
         ((node = do_QueryInterface(mTarget)) &&
          (node == node->OwnerDoc() ||
           node == node->OwnerDoc()->GetRootElement() ||
           node == node->OwnerDoc()->GetBody()))) {
       flags.mPassive = true;

--- a/dom/events/EventStateManager.cpp
+++ b/dom/events/EventStateManager.cpp
@@ -53,17 +53,16 @@
 #include "nsPIWindowRoot.h"
 #include "nsIWebNavigation.h"
 #include "nsIContentViewer.h"
 #include "nsFrameManager.h"
 #include "nsITabChild.h"
 #include "nsPluginFrame.h"
 #include "nsMenuPopupFrame.h"
 
-#include "nsIDOMXULElement.h"
 #include "nsIObserverService.h"
 #include "nsIDocShell.h"
 #include "nsIMozBrowserFrame.h"
 
 #include "nsSubDocumentFrame.h"
 #include "nsLayoutUtils.h"
 #include "nsIInterfaceRequestorUtils.h"
 #include "nsUnicharUtils.h"

--- a/dom/fetch/BodyExtractor.cpp
+++ b/dom/fetch/BodyExtractor.cpp
@@ -5,19 +5,19 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "BodyExtractor.h"
 #include "mozilla/dom/File.h"
 #include "mozilla/dom/FormData.h"
 #include "mozilla/dom/TypedArray.h"
 #include "mozilla/dom/URLSearchParams.h"
 #include "mozilla/dom/XMLHttpRequest.h"
+#include "mozilla/UniquePtr.h"
 #include "nsContentUtils.h"
-#include "nsIDOMDocument.h"
-#include "nsIDOMSerializer.h"
+#include "nsDOMSerializer.h"
 #include "nsIGlobalObject.h"
 #include "nsIInputStream.h"
 #include "nsIOutputStream.h"
 #include "nsIStorageStream.h"
 #include "nsStringStream.h"
 
 namespace mozilla {
 namespace dom {
@@ -68,18 +68,17 @@ BodyExtractor<const ArrayBufferView>::Ge
 }
 
 template<> nsresult
 BodyExtractor<nsIDocument>::GetAsStream(nsIInputStream** aResult,
                                         uint64_t* aContentLength,
                                         nsACString& aContentTypeWithCharset,
                                         nsACString& aCharset) const
 {
-  nsCOMPtr<nsIDOMDocument> domdoc(do_QueryInterface(mBody));
-  NS_ENSURE_STATE(domdoc);
+  NS_ENSURE_STATE(mBody);
   aCharset.AssignLiteral("UTF-8");
 
   nsresult rv;
   nsCOMPtr<nsIStorageStream> storStream;
   rv = NS_NewStorageStream(4096, UINT32_MAX, getter_AddRefs(storStream));
   NS_ENSURE_SUCCESS(rv, rv);
 
   nsCOMPtr<nsIOutputStream> output;
@@ -102,23 +101,25 @@ BodyExtractor<nsIDocument>::GetAsStream(
     uint32_t written;
     rv = output->Write(utf8Serialized.get(), utf8Serialized.Length(), &written);
     NS_ENSURE_SUCCESS(rv, rv);
 
     MOZ_ASSERT(written == utf8Serialized.Length());
   } else {
     aContentTypeWithCharset.AssignLiteral("application/xml;charset=UTF-8");
 
-    nsCOMPtr<nsIDOMSerializer> serializer =
-      do_CreateInstance(NS_XMLSERIALIZER_CONTRACTID, &rv);
-    NS_ENSURE_SUCCESS(rv, rv);
+    auto serializer = MakeUnique<nsDOMSerializer>();
 
     // Make sure to use the encoding we'll send
-    rv = serializer->SerializeToStream(domdoc, output, aCharset);
-    NS_ENSURE_SUCCESS(rv, rv);
+    ErrorResult res;
+    serializer->SerializeToStream(*mBody, output, NS_LITERAL_STRING("UTF-8"),
+                                  res);
+    if (NS_WARN_IF(res.Failed())) {
+      return res.StealNSResult();
+    }
   }
 
   output->Close();
 
   uint32_t length;
   rv = storStream->GetLength(&length);
   NS_ENSURE_SUCCESS(rv, rv);
   *aContentLength = length;

--- a/dom/fetch/moz.build
+++ b/dom/fetch/moz.build
@@ -43,16 +43,18 @@ UNIFIED_SOURCES += [
 ]
 
 IPDL_SOURCES += [
     'ChannelInfo.ipdlh',
     'FetchTypes.ipdlh',
 ]
 
 LOCAL_INCLUDES += [
+    # For nsDOMSerializer
+    '/dom/base',
     # For HttpBaseChannel.h dependencies
     '/netwerk/base',
     # For nsDataHandler.h
     '/netwerk/protocol/data',
     # For HttpBaseChannel.h
     '/netwerk/protocol/http',
 ]
 

--- a/dom/html/HTMLMediaElement.cpp
+++ b/dom/html/HTMLMediaElement.cpp
@@ -1803,16 +1803,17 @@ void HTMLMediaElement::AbortExistingLoad
   mHaveQueuedSelectResource = false;
   mSuspendedForPreloadNone = false;
   mDownloadSuspendedByCache = false;
   mMediaInfo = MediaInfo();
   mIsEncrypted = false;
   mPendingEncryptedInitData.Reset();
   mWaitingForKey = NOT_WAITING_FOR_KEY;
   mSourcePointer = nullptr;
+  mAttemptPlayUponLoadedMetadata = false;
 
   mTags = nullptr;
 
   if (mNetworkState != NETWORK_EMPTY) {
     NS_ASSERTION(!mDecoder && !mSrcStream, "How did someone setup a new stream/decoder already?");
     // ChangeNetworkState() will call UpdateAudioChannelPlayingState()
     // indirectly which depends on mPaused. So we need to update mPaused first.
     if (!mPaused) {
@@ -3951,17 +3952,17 @@ void
 HTMLMediaElement::NotifyXPCOMShutdown()
 {
   ShutdownDecoder();
 }
 
 already_AddRefed<Promise>
 HTMLMediaElement::Play(ErrorResult& aRv)
 {
-  LOG(LogLevel::Debug, ("%p Play() called by JS", this));
+  LOG(LogLevel::Debug, ("%p Play() called by JS readyState=%d", this, mReadyState));
 
   if (mAudioChannelWrapper && mAudioChannelWrapper->IsPlaybackBlocked()) {
     MaybeDoLoad();
 
     // A blocked media element will be resumed later, so we return a pending
     // promise which might be resolved/rejected depends on the result of
     // resuming the blocked media element.
     RefPtr<Promise> promise = CreateDOMPromise(aRv);
@@ -3990,17 +3991,22 @@ HTMLMediaElement::PlayInternal(ErrorResu
 
   // 4.8.12.8
   // When the play() method on a media element is invoked, the user agent must
   // run the following steps.
 
   // 4.8.12.8 - Step 1:
   // If the media element is not allowed to play, return a promise rejected
   // with a "NotAllowedError" DOMException and abort these steps.
-  if (!IsAllowedToPlay()) {
+  // Note: IsAllowedToPlay() needs to know whether there is an audio track
+  // in the resource, and for that we need to be at readyState HAVE_METADATA
+  // or above. So only reject here if we're at readyState HAVE_METADATA. If
+  // we're below that, we'll we delay fulfilling the play promise until we've
+  // reached readyState >= HAVE_METADATA below.
+  if (mReadyState >= HAVE_METADATA && !IsAllowedToPlay()) {
     // NOTE: for promise-based-play, will return a rejected promise here.
     LOG(LogLevel::Debug,
         ("%p Play() promise rejected because not allowed to play.", this));
     aRv.Throw(NS_ERROR_DOM_MEDIA_NOT_ALLOWED_ERR);
     return nullptr;
   }
 
   // 4.8.12.8 - Step 2:
@@ -4048,31 +4054,40 @@ HTMLMediaElement::PlayInternal(ErrorResu
 
   // Even if we just did Load() or ResumeLoad(), we could already have a decoder
   // here if we managed to clone an existing decoder.
   if (mDecoder) {
     if (mDecoder->IsEnded()) {
       SetCurrentTime(0);
     }
     if (!mPausedForInactiveDocumentOrChannel) {
-      nsresult rv = mDecoder->Play();
-      if (NS_FAILED(rv)) {
-        // We don't need to remove the _promise_ from _mPendingPlayPromises_ here.
-        // If something wrong between |mPendingPlayPromises.AppendElement(promise);|
-        // and here, the _promise_ should already have been rejected. Otherwise,
-        // the _promise_ won't be returned to JS at all, so just leave it in the
-        // _mPendingPlayPromises_ and let it be resolved/rejected with the
-        // following actions and the promise-resolution won't be observed at all.
-        LOG(LogLevel::Debug,
-            ("%p Play() promise rejected because failed to play MediaDecoder.",
-             this));
-        aRv.Throw(rv);
-        return nullptr;
+      if (mReadyState < HAVE_METADATA) {
+        // We don't know whether the autoplay policy will allow us to play yet,
+        // as we don't yet know whether the media has audio tracks. So delay
+        // starting playback until we've loaded metadata.
+        mAttemptPlayUponLoadedMetadata = true;
+      } else {
+        nsresult rv = mDecoder->Play();
+        if (NS_FAILED(rv)) {
+          // We don't need to remove the _promise_ from _mPendingPlayPromises_ here.
+          // If something wrong between |mPendingPlayPromises.AppendElement(promise);|
+          // and here, the _promise_ should already have been rejected. Otherwise,
+          // the _promise_ won't be returned to JS at all, so just leave it in the
+          // _mPendingPlayPromises_ and let it be resolved/rejected with the
+          // following actions and the promise-resolution won't be observed at all.
+          LOG(LogLevel::Debug,
+              ("%p Play() promise rejected because failed to play MediaDecoder.",
+              this));
+          aRv.Throw(rv);
+          return nullptr;
+        }
       }
     }
+  } else if (mReadyState < HAVE_METADATA) {
+    mAttemptPlayUponLoadedMetadata = true;
   }
 
   if (mCurrentPlayRangeStart == -1.0) {
     mCurrentPlayRangeStart = CurrentTime();
   }
 
   const bool oldPaused = mPaused;
   mPaused = false;
@@ -4921,17 +4936,17 @@ HTMLMediaElement::FinishDecoderSetup(Med
   // This will also do an AddRemoveSelfReference.
   NotifyOwnerDocumentActivityChanged();
 
   if (mPausedForInactiveDocumentOrChannel) {
     mDecoder->Suspend();
   }
 
   nsresult rv = NS_OK;
-  if (!mPaused) {
+  if (!mPaused && !mAttemptPlayUponLoadedMetadata) {
     SetPlayedOrSeeked(true);
     if (!mPausedForInactiveDocumentOrChannel) {
       rv = mDecoder->Play();
     }
   }
 
   if (NS_FAILED(rv)) {
     ShutdownDecoder();
@@ -5925,16 +5940,25 @@ HTMLMediaElement::ChangeReadyState(nsMed
     DispatchAsyncEvent(NS_LITERAL_STRING("loadeddata"));
     mLoadedDataFired = true;
   }
 
   if (oldState < HAVE_FUTURE_DATA &&
       mReadyState >= HAVE_FUTURE_DATA) {
     DispatchAsyncEvent(NS_LITERAL_STRING("canplay"));
     if (!mPaused) {
+      if (mAttemptPlayUponLoadedMetadata && mDecoder) {
+        mAttemptPlayUponLoadedMetadata = false;
+        if (IsAllowedToPlay()) {
+          mDecoder->Play();
+        } else {
+          AsyncRejectPendingPlayPromises(NS_ERROR_DOM_MEDIA_NOT_ALLOWED_ERR);
+          mPaused = true;
+        }
+      }
       NotifyAboutPlaying();
     }
   }
 
   CheckAutoplayDataReady();
 
   if (oldState < HAVE_ENOUGH_DATA &&
       mReadyState >= HAVE_ENOUGH_DATA) {
@@ -6045,16 +6069,17 @@ void HTMLMediaElement::CheckAutoplayData
   UpdateSrcMediaStreamPlaying();
   UpdateAudioChannelPlayingState();
 
   if (mDecoder) {
     SetPlayedOrSeeked(true);
     if (mCurrentPlayRangeStart == -1.0) {
       mCurrentPlayRangeStart = CurrentTime();
     }
+    MOZ_ASSERT(!mAttemptPlayUponLoadedMetadata);
     mDecoder->Play();
   } else if (mSrcStream) {
     SetPlayedOrSeeked(true);
   }
 
   // For blocked media, the event would be pending until it is resumed.
   DispatchAsyncEvent(NS_LITERAL_STRING("play"));
 
@@ -6382,16 +6407,17 @@ void HTMLMediaElement::SuspendOrResumeEl
         mDecoder->Pause();
         mDecoder->Suspend();
       }
       mEventDeliveryPaused = aSuspendEvents;
     } else {
       if (mDecoder) {
         mDecoder->Resume();
         if (!mPaused && !mDecoder->IsEnded()) {
+          MOZ_ASSERT(!mAttemptPlayUponLoadedMetadata);
           mDecoder->Play();
         }
       }
       if (mEventDeliveryPaused) {
         mEventDeliveryPaused = false;
         DispatchPendingMediaEvents();
       }
     }

--- a/dom/html/HTMLMediaElement.h
+++ b/dom/html/HTMLMediaElement.h
@@ -1814,16 +1814,23 @@ private:
   // True if media element has been marked as 'tainted' and can't
   // participate in video decoder suspending.
   bool mHasSuspendTaint = false;
 
   // True if media element has been forced into being considered 'hidden'.
   // For use by mochitests. Enabling pref "media.test.video-suspend"
   bool mForcedHidden = false;
 
+  // True if we attempted to play before the media element had loaded
+  // metadata, and we need to attempt the play once we reach loaded metadata.
+  // If autoplay is disabled, we can't decide whether to allow a play()
+  // until we've loaded metadata, as we need to know whether the resource
+  // has an audio track.
+  bool mAttemptPlayUponLoadedMetadata = false;
+
   // True if audio tracks and video tracks are constructed and added into the
   // track list, false if all tracks are removed from the track list.
   bool mMediaTracksConstructed = false;
 
   Visibility mVisibilityState = Visibility::UNTRACKED;
 
   UniquePtr<ErrorSink> mErrorSink;
 

--- a/dom/interfaces/core/moz.build
+++ b/dom/interfaces/core/moz.build
@@ -9,13 +9,12 @@ with Files("**"):
 
 XPIDL_SOURCES += [
     'nsIDOMDocument.idl',
     'nsIDOMDocumentFragment.idl',
     'nsIDOMElement.idl',
     'nsIDOMNode.idl',
     'nsIDOMNodeList.idl',
     'nsIDOMNSEditableElement.idl',
-    'nsIDOMXMLDocument.idl',
 ]
 
 XPIDL_MODULE = 'dom_core'
 

deleted file mode 100644
--- a/dom/interfaces/core/nsIDOMXMLDocument.idl
+++ /dev/null
@@ -1,15 +0,0 @@
-/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* 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 "nsISupports.idl"
-
-// The only reason this interface still exists is that we have addon and Firefox
-// code QIing to it and using it for instanceof via Components.interfaces, and
-// the interface needs to exist in order for the shim stuff in
-// xpcom/reflect/xptinfo/ShimInterfaceInfo.cpp to work.
-[uuid(89ab39cb-c568-4d85-bd34-306d5cd5164d)]
-interface nsIDOMXMLDocument : nsISupports
-{
-};

--- a/dom/interfaces/xul/moz.build
+++ b/dom/interfaces/xul/moz.build
@@ -9,17 +9,16 @@ with Files("**"):
 
 XPIDL_SOURCES += [
     'nsIDOMXULButtonElement.idl',
     'nsIDOMXULCheckboxElement.idl',
     'nsIDOMXULCommandDispatcher.idl',
     'nsIDOMXULContainerElement.idl',
     'nsIDOMXULControlElement.idl',
     'nsIDOMXULDescriptionElement.idl',
-    'nsIDOMXULElement.idl',
     'nsIDOMXULLabeledControlEl.idl',
     'nsIDOMXULLabelElement.idl',
     'nsIDOMXULMenuListElement.idl',
     'nsIDOMXULMultSelectCntrlEl.idl',
     'nsIDOMXULRelatedElement.idl',
     'nsIDOMXULSelectCntrlEl.idl',
     'nsIDOMXULSelectCntrlItemEl.idl',
     'nsIDOMXULTextboxElement.idl',

--- a/dom/interfaces/xul/nsIDOMXULContainerElement.idl
+++ b/dom/interfaces/xul/nsIDOMXULContainerElement.idl
@@ -1,68 +1,22 @@
 /* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* 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 "nsIDOMXULElement.idl"
+#include "nsISupports.idl"
 interface nsIDOMXULContainerElement;
 
 [scriptable, uuid(800a68c7-b854-4597-a436-3055ce5c5c96)]
 interface nsIDOMXULContainerItemElement : nsISupports
 {
   /**
    * Returns the parent container if any.
    */
   readonly attribute nsIDOMXULContainerElement parentContainer;
 };
 
 [scriptable, uuid(b2bc96b8-31fc-42f4-937a-bd27291af40b)]
 interface nsIDOMXULContainerElement : nsIDOMXULContainerItemElement
 {
-  /**
-   * Creates an item for the given label and value and appends it to the
-   * container.
-   *
-   * @param aLabel - the label for the new item
-   * @param aValue - the value of the new item
-   */
-  nsIDOMXULElement appendItem(in DOMString aLabel, in DOMString aValue);
-
-  /**
-   * Creates an item for the given label and value and inserts it into the
-   * container at the specified position.
-   *
-   * @param aIndex - the index where the new item will be inserted
-   * @param aLabel - the label for the new item
-   * @param aValue - the value of the new item
-   */
-  nsIDOMXULElement insertItemAt(in long aIndex, in DOMString aLabel,
-                                in DOMString aValue);
-
-  /**
-   * Removes an item from the container.
-   *
-   * @param aIndex - index of the item to remove
-   */
-  nsIDOMXULElement removeItemAt(in long aIndex);
-
-  /**
-   * Returns a count of items in the container.
-   */
-  readonly attribute unsigned long itemCount;
-
-  /**
-   * Returns the index of an item or -1 if the item is not in the container.
-   *
-   * @param aItem - the item to determine the index of
-   */
-  long getIndexOfItem(in nsIDOMXULElement aItem);
-
-  /**
-   * Returns the item at a given index or null if the item is not is the
-   * container.
-   *
-   * @param aIndex - the index of the item to return
-   */
-  nsIDOMXULElement getItemAtIndex(in long aIndex);
 };
 

--- a/dom/interfaces/xul/nsIDOMXULControlElement.idl
+++ b/dom/interfaces/xul/nsIDOMXULControlElement.idl
@@ -1,15 +1,14 @@
 /* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* 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 "nsIDOMElement.idl"
-#include "nsIDOMXULElement.idl"
+#include "nsISupports.idl"
 
 interface nsIControllers;
 
 [scriptable, uuid(ea7f92d0-b379-4107-91b4-1e69bdd771e3)]
 interface nsIDOMXULControlElement : nsISupports {
   attribute boolean disabled;
   attribute long tabIndex;
   

--- a/dom/interfaces/xul/nsIDOMXULDescriptionElement.idl
+++ b/dom/interfaces/xul/nsIDOMXULDescriptionElement.idl
@@ -1,15 +1,15 @@
 
 /* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* 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 "nsIDOMXULElement.idl"
+#include "nsISupports.idl"
 
 [scriptable, uuid(64c3500e-e258-4d49-b7ca-c93ab0931ce4)]
 interface nsIDOMXULDescriptionElement : nsISupports {
   attribute boolean disabled;
   attribute boolean crop;
   attribute DOMString value;
 };
 

deleted file mode 100644
--- a/dom/interfaces/xul/nsIDOMXULElement.idl
+++ /dev/null
@@ -1,17 +0,0 @@
-/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* 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 "nsIDOMElement.idl"
-
-interface nsIRDFCompositeDataSource;
-interface nsIRDFResource;
-interface nsIControllers;
-interface nsIBoxObject;
-
-
-[uuid(75435ab3-6863-42a1-ade3-025393d9e80e)]
-interface nsIDOMXULElement : nsIDOMElement
-{
-};

--- a/dom/interfaces/xul/nsIDOMXULMenuListElement.idl
+++ b/dom/interfaces/xul/nsIDOMXULMenuListElement.idl
@@ -1,15 +1,16 @@
 /* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* 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 "nsIDOMXULSelectCntrlEl.idl"
 interface nsIDOMXULTextBoxElement;
+interface nsIDOMNode;
 
 [scriptable, uuid(36c16a17-c0e9-4b35-951b-81a147314ef1)]
 interface nsIDOMXULMenuListElement : nsIDOMXULSelectControlElement {
   attribute boolean editable;
   attribute boolean open;
   
   // label of selected option or value of textfield for editable menu lists
   readonly attribute DOMString label;

--- a/dom/interfaces/xul/nsIDOMXULMultSelectCntrlEl.idl
+++ b/dom/interfaces/xul/nsIDOMXULMultSelectCntrlEl.idl
@@ -1,15 +1,17 @@
 /* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* 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 "nsIDOMXULSelectCntrlEl.idl"
 
+interface nsIDOMNodeList;
+
 [scriptable, uuid(40654a10-8204-4f06-9f21-7baa31c7b1dd)]
 interface nsIDOMXULMultiSelectControlElement : nsIDOMXULSelectControlElement
 {
   attribute DOMString selType;
 
   attribute nsIDOMXULSelectControlItemElement currentItem;
   attribute long currentIndex;
 

--- a/dom/interfaces/xul/nsIDOMXULSelectCntrlItemEl.idl
+++ b/dom/interfaces/xul/nsIDOMXULSelectCntrlItemEl.idl
@@ -1,14 +1,14 @@
 /* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* 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 "nsIDOMXULElement.idl"
+#include "nsISupports.idl"
 interface nsIDOMXULSelectControlElement;
 
 [scriptable, uuid(5c6be58f-17df-4750-88a5-4a59ac28adc9)]
 interface nsIDOMXULSelectControlItemElement : nsISupports {
   attribute boolean disabled;
   attribute DOMString crop;
   attribute DOMString image;
   attribute DOMString label;

--- a/dom/interfaces/xul/nsIDOMXULTreeElement.idl
+++ b/dom/interfaces/xul/nsIDOMXULTreeElement.idl
@@ -1,18 +1,18 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 /* 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 "nsIDOMXULElement.idl"
-#include "nsIDOMElement.idl"
+#include "nsISupports.idl"
 
 interface nsITreeColumns;
 interface nsITreeView;
+interface nsIDOMElement;
 interface nsIDOMXULTextBoxElement;
 
 /**
  * @status UNDER_DEVELOPMENT
  */
 
 [scriptable, uuid(013b62af-1e2f-4b07-9091-d7c0fc4687e2)]
 interface nsIDOMXULTreeElement : nsISupports

--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -3185,27 +3185,36 @@ ContentParent::KillHard(const char* aRea
       NS_LITERAL_CSTRING("ipc_channel_error"),
       reason);
 
     Telemetry::Accumulate(Telemetry::SUBPROCESS_KILL_HARD, reason, 1);
 
     RefPtr<ContentParent> self = this;
     std::function<void(bool)> callback = [self](bool aResult) {
       self->OnGenerateMinidumpComplete(aResult);
+      MessageChannel* channel = self->GetIPCChannel();
+      if (channel) {
+        channel->Close();
+      }
     };
     // Generate the report and insert into the queue for submittal.
     mCrashReporter->GenerateMinidumpAndPair(Process(),
                                             nullptr,
                                             NS_LITERAL_CSTRING("browser"),
                                             Move(callback),
                                             true);
     return;
   }
 
   OnGenerateMinidumpComplete(false);
+
+  MessageChannel* channel = GetIPCChannel();
+  if (channel) {
+    channel->Close();
+  }
 }
 
 void
 ContentParent::OnGenerateMinidumpComplete(bool aDumpResult)
 {
   if (mCrashReporter && aDumpResult) {
     // CrashReporterHost::GenerateMinidumpAndPair() is successful.
     mCreatedPairedMinidumps = mCrashReporter->FinalizeCrashReport();

--- a/dom/ipc/PBrowser.ipdl
+++ b/dom/ipc/PBrowser.ipdl
@@ -64,16 +64,17 @@ using class mozilla::WidgetTouchEvent fr
 using class mozilla::WidgetPluginEvent from "ipc/nsGUIEventIPC.h";
 using struct mozilla::dom::RemoteDOMEvent from "mozilla/dom/TabMessageUtils.h";
 using struct mozilla::layers::TextureFactoryIdentifier from "mozilla/layers/CompositorTypes.h";
 using mozilla::layers::CompositorOptions from "mozilla/layers/CompositorOptions.h";
 using mozilla::CSSToScreenScale from "Units.h";
 using mozilla::CommandInt from "mozilla/EventForwards.h";
 using mozilla::WritingMode from "mozilla/WritingModes.h";
 using nsIWidget::TouchPointerState from "nsIWidget.h";
+using nsCursor from "nsIWidget.h";
 using struct LookAndFeelInt from "mozilla/widget/WidgetMessageUtils.h";
 using class mozilla::dom::MessagePort from "mozilla/dom/MessagePort.h";
 using class mozilla::dom::ipc::StructuredCloneData from "mozilla/dom/ipc/StructuredCloneData.h";
 using mozilla::EventMessage from "mozilla/EventForwards.h";
 using nsEventStatus from "mozilla/EventForwards.h";
 using mozilla::Modifiers from "mozilla/EventForwards.h";
 using nsSizeMode from "nsIWidgetListener.h";
 using mozilla::widget::CandidateWindowPosition from "ipc/nsGUIEventIPC.h";
@@ -361,17 +362,17 @@ parent:
     /**
      * Set the native cursor.
      * @param value
      *   The widget cursor to set.
      * @param force
      *   Invalidate any locally cached cursor settings and force an
      *   update.
      */
-    async SetCursor(uint32_t value, bool force);
+    async SetCursor(nsCursor value, bool force);
 
     /**
      * Set the native cursor using a custom image.
      * @param cursorData
      *   Serialized image data.
      * @param width
      *   Width of the image.
      * @param height

--- a/dom/ipc/TabParent.cpp
+++ b/dom/ipc/TabParent.cpp
@@ -131,18 +131,17 @@ namespace mozilla {
 namespace dom {
 
 TabParent::LayerToTabParentTable* TabParent::sLayerToTabParentTable = nullptr;
 
 NS_IMPL_ISUPPORTS(TabParent,
                   nsITabParent,
                   nsIAuthPromptProvider,
                   nsISecureBrowserUI,
-                  nsISupportsWeakReference,
-                  nsIWebBrowserPersistable)
+                  nsISupportsWeakReference)
 
 TabParent::TabParent(nsIContentParent* aManager,
                      const TabId& aTabId,
                      const TabContext& aContext,
                      uint32_t aChromeFlags)
   : TabContext(aContext)
   , mFrameElement(nullptr)
   , mContentCache(*this)
@@ -1717,19 +1716,19 @@ TabParent::RecvAsyncMessage(const nsStri
   CrossProcessCpowHolder cpows(Manager(), aCpows);
   if (!ReceiveMessage(aMessage, false, &data, &cpows, aPrincipal, nullptr)) {
     return IPC_FAIL_NO_REASON(this);
   }
   return IPC_OK();
 }
 
 mozilla::ipc::IPCResult
-TabParent::RecvSetCursor(const uint32_t& aCursor, const bool& aForce)
+TabParent::RecvSetCursor(const nsCursor& aCursor, const bool& aForce)
 {
-  mCursor = static_cast<nsCursor>(aCursor);
+  mCursor = aCursor;
   mCustomCursor = nullptr;
 
   nsCOMPtr<nsIWidget> widget = GetWidget();
   if (widget) {
     if (aForce) {
       widget->ClearCachedCursor();
     }
     if (mTabSetsCursor) {
@@ -3432,29 +3431,33 @@ TabParent::TakeDragVisualization(RefPtr<
 
 bool
 TabParent::AsyncPanZoomEnabled() const
 {
   nsCOMPtr<nsIWidget> widget = GetWidget();
   return widget && widget->AsyncPanZoomEnabled();
 }
 
-NS_IMETHODIMP
+void
 TabParent::StartPersistence(uint64_t aOuterWindowID,
-                            nsIWebBrowserPersistDocumentReceiver* aRecv)
+                            nsIWebBrowserPersistDocumentReceiver* aRecv,
+                            ErrorResult& aRv)
 {
   nsCOMPtr<nsIContentParent> manager = Manager();
   if (!manager->IsContentParent()) {
-    return NS_ERROR_UNEXPECTED;
+    aRv.Throw(NS_ERROR_UNEXPECTED);
+    return;
   }
   auto* actor = new WebBrowserPersistDocumentParent();
   actor->SetOnReady(aRecv);
-  return manager->AsContentParent()
-    ->SendPWebBrowserPersistDocumentConstructor(actor, this, aOuterWindowID)
-    ? NS_OK : NS_ERROR_FAILURE;
+  bool ok = manager->AsContentParent()
+    ->SendPWebBrowserPersistDocumentConstructor(actor, this, aOuterWindowID);
+  if (!ok) {
+    aRv.Throw(NS_ERROR_FAILURE);
+  }
   // (The actor will be destroyed on constructor failure.)
 }
 
 NS_IMETHODIMP
 TabParent::StartApzAutoscroll(float aAnchorX, float aAnchorY,
                               nsViewID aScrollId, uint32_t aPresShellId,
                               bool* aOutRetval)
 {

--- a/dom/ipc/TabParent.h
+++ b/dom/ipc/TabParent.h
@@ -22,29 +22,29 @@
 #include "mozilla/Move.h"
 #include "nsCOMPtr.h"
 #include "nsIAuthPromptProvider.h"
 #include "nsIBrowserDOMWindow.h"
 #include "nsIDOMEventListener.h"
 #include "nsIKeyEventInPluginCallback.h"
 #include "nsISecureBrowserUI.h"
 #include "nsITabParent.h"
-#include "nsIWebBrowserPersistable.h"
 #include "nsIXULBrowserWindow.h"
 #include "nsRefreshDriver.h"
 #include "nsWeakReference.h"
 #include "Units.h"
 #include "nsIWidget.h"
 
 class nsFrameLoader;
 class nsIContent;
 class nsIPrincipal;
 class nsIURI;
 class nsILoadContext;
 class nsIDocShell;
+class nsIWebBrowserPersistDocumentReceiver;
 
 namespace mozilla {
 
 namespace a11y {
 class DocAccessibleParent;
 }
 
 namespace jsipc {
@@ -82,17 +82,16 @@ class StructuredCloneData;
 class TabParent final : public PBrowserParent
                       , public nsIDOMEventListener
                       , public nsITabParent
                       , public nsIAuthPromptProvider
                       , public nsISecureBrowserUI
                       , public nsIKeyEventInPluginCallback
                       , public nsSupportsWeakReference
                       , public TabContext
-                      , public nsIWebBrowserPersistable
                       , public LiveResizeListener
 {
   typedef mozilla::dom::ClonedMessageData ClonedMessageData;
 
   virtual ~TabParent();
 
 public:
   // Helper class for ContentParent::RecvCreateWindow.
@@ -268,18 +267,18 @@ public:
     const bool& aIsVertical,
     const LayoutDeviceIntPoint& aPoint) override;
 
   virtual mozilla::ipc::IPCResult
   RecvEnableDisableCommands(const nsString& aAction,
                             nsTArray<nsCString>&& aEnabledCommands,
                             nsTArray<nsCString>&& aDisabledCommands) override;
 
-  virtual mozilla::ipc::IPCResult
-  RecvSetCursor(const uint32_t& aValue, const bool& aForce) override;
+  virtual mozilla::ipc::IPCResult RecvSetCursor(const nsCursor& aValue,
+                                                const bool& aForce) override;
 
   virtual mozilla::ipc::IPCResult RecvSetCustomCursor(const nsCString& aUri,
                                                       const uint32_t& aWidth,
                                                       const uint32_t& aHeight,
                                                       const uint32_t& aStride,
                                                       const uint8_t& aFormat,
                                                       const uint32_t& aHotspotX,
                                                       const uint32_t& aHotspotY,
@@ -485,17 +484,20 @@ public:
                                     PIndexedDBPermissionRequestParent* aActor)
                                     override;
 
   bool GetGlobalJSObject(JSContext* cx, JSObject** globalp);
 
   NS_DECL_ISUPPORTS
   NS_DECL_NSIAUTHPROMPTPROVIDER
   NS_DECL_NSISECUREBROWSERUI
-  NS_DECL_NSIWEBBROWSERPERSISTABLE
+
+  void StartPersistence(uint64_t aOuterWindowID,
+                        nsIWebBrowserPersistDocumentReceiver* aRecv,
+                        ErrorResult& aRv);
 
   bool HandleQueryContentEvent(mozilla::WidgetQueryContentEvent& aEvent);
 
   bool SendPasteTransferable(const IPCDataTransfer& aDataTransfer,
                              const bool& aIsPrivateData,
                              const IPC::Principal& aRequestingPrincipal,
                              const uint32_t& aContentPolicyType);
 

--- a/dom/media/ChannelMediaDecoder.cpp
+++ b/dom/media/ChannelMediaDecoder.cpp
@@ -162,19 +162,19 @@ ChannelMediaDecoder::NotifyPrincipalChan
     // We'll receive one notification when the channel's initial principal
     // is known, after all HTTP redirects have resolved. This isn't really a
     // principal change, so return here to avoid the mSameOriginMedia check
     // below.
     mInitialChannelPrincipalKnown = true;
     return;
   }
   if (!mSameOriginMedia &&
-      DecoderTraits::CrossOriginRedirectsProhibited(ContainerType())) {
-    // For some content types we block mid-flight channel redirects to cross
-    // origin destinations due to security constraints. See bug 1441153.
+      Preferences::GetBool("media.block-midflight-redirects", true)) {
+    // Block mid-flight redirects to non CORS same origin destinations.
+    // See bugs 1441153, 1443942.
     LOG("ChannnelMediaDecoder prohibited cross origin redirect blocked.");
     NetworkError(MediaResult(NS_ERROR_DOM_BAD_URI,
                              "Prohibited cross origin redirect blocked"));
   }
 }
 
 void
 ChannelMediaDecoder::ResourceCallback::NotifySuspendedStatusChanged(

--- a/dom/media/ChannelMediaResource.cpp
+++ b/dom/media/ChannelMediaResource.cpp
@@ -280,16 +280,21 @@ ChannelMediaResource::OnStartRequest(nsI
     // Not an HTTP channel. Assume data will be sent from position zero.
     startOffset = 0;
   }
 
   // Update principals before OnDataAvailable() putting the data in the cache.
   // This is important, we want to make sure all principals are updated before
   // any consumer can see the new data.
   UpdatePrincipal();
+  if (owner->HasError()) {
+    // Updating the principal resulted in an error. Abort the load.
+    CloseChannel();
+    return NS_OK;
+  }
 
   mCacheStream.NotifyDataStarted(mLoadID, startOffset, seekable, length);
   mIsTransportSeekable = seekable;
 
   mSuspendAgent.Delegate(mChannel);
 
   // Fires an initial progress event.
   owner->DownloadProgressed();
@@ -312,17 +317,17 @@ ChannelMediaResource::IsTransportSeekabl
   MOZ_ASSERT(NS_IsMainThread());
   return mIsTransportSeekable;
 }
 
 nsresult
 ChannelMediaResource::ParseContentRangeHeader(nsIHttpChannel * aHttpChan,
                                               int64_t& aRangeStart,
                                               int64_t& aRangeEnd,
-                                              int64_t& aRangeTotal)
+                                              int64_t& aRangeTotal) const
 {
   NS_ENSURE_ARG(aHttpChan);
 
   nsAutoCString rangeStr;
   nsresult rv = aHttpChan->GetResponseHeader(NS_LITERAL_CSTRING("Content-Range"),
                                              rangeStr);
   NS_ENSURE_SUCCESS(rv, rv);
   NS_ENSURE_FALSE(rangeStr.IsEmpty(), NS_ERROR_ILLEGAL_VALUE);
@@ -441,40 +446,82 @@ ChannelMediaResource::OnDataAvailable(ui
       return rv;
     NS_ASSERTION(read > 0, "Read 0 bytes while data was available?");
     count -= read;
   }
 
   return NS_OK;
 }
 
+int64_t
+ChannelMediaResource::CalculateStreamLength() const
+{
+  if (!mChannel) {
+    return -1;
+  }
+
+  nsCOMPtr<nsIHttpChannel> hc = do_QueryInterface(mChannel);
+  if (!hc) {
+    return -1;
+  }
+
+  bool succeeded = false;
+  Unused << hc->GetRequestSucceeded(&succeeded);
+  if (!succeeded) {
+    return -1;
+  }
+
+  // We can't determine the length of uncompressed payload.
+  const bool isCompressed = IsPayloadCompressed(hc);
+  if (isCompressed) {
+    return -1;
+  }
+
+  int64_t contentLength = -1;
+  if (NS_FAILED(hc->GetContentLength(&contentLength))) {
+    return -1;
+  }
+
+  uint32_t responseStatus = 0;
+  Unused << hc->GetResponseStatus(&responseStatus);
+  if (responseStatus != HTTP_PARTIAL_RESPONSE_CODE) {
+    return contentLength;
+  }
+
+  // We have an HTTP Byte Range response. The Content-Length is the length
+  // of the response, not the resource. We need to parse the Content-Range
+  // header and extract the range total in order to get the stream length.
+  int64_t rangeStart = 0;
+  int64_t rangeEnd = 0;
+  int64_t rangeTotal = 0;
+  bool gotRangeHeader = NS_SUCCEEDED(
+    ParseContentRangeHeader(hc, rangeStart, rangeEnd, rangeTotal));
+  if (gotRangeHeader && rangeTotal != -1) {
+    contentLength = std::max(contentLength, rangeTotal);
+  }
+  return contentLength;
+}
+
 nsresult
 ChannelMediaResource::Open(nsIStreamListener** aStreamListener)
 {
   NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");
   MOZ_ASSERT(aStreamListener);
   MOZ_ASSERT(mChannel);
 
-  int64_t cl = -1;
-  nsCOMPtr<nsIHttpChannel> hc = do_QueryInterface(mChannel);
-  if (hc && !IsPayloadCompressed(hc)) {
-    if (NS_FAILED(hc->GetContentLength(&cl))) {
-      cl = -1;
-    }
-  }
-
-  nsresult rv = mCacheStream.Init(cl);
+  int64_t streamLength = CalculateStreamLength();
+  nsresult rv = mCacheStream.Init(streamLength);
   if (NS_FAILED(rv)) {
     return rv;
   }
 
   mSharedInfo = new SharedInfo;
   mSharedInfo->mResources.AppendElement(this);
 
-  mIsLiveStream = cl < 0;
+  mIsLiveStream = streamLength < 0;
   mListener = new Listener(this, 0, ++mLoadID);
   *aStreamListener = mListener;
   NS_ADDREF(*aStreamListener);
   return NS_OK;
 }
 
 nsresult
 ChannelMediaResource::OpenChannel(int64_t aOffset)

--- a/dom/media/ChannelMediaResource.h
+++ b/dom/media/ChannelMediaResource.h
@@ -226,17 +226,21 @@ protected:
   void UpdatePrincipal();
 
   // Parses 'Content-Range' header and returns results via parameters.
   // Returns error if header is not available, values are not parse-able or
   // values are out of range.
   nsresult ParseContentRangeHeader(nsIHttpChannel * aHttpChan,
                                    int64_t& aRangeStart,
                                    int64_t& aRangeEnd,
-                                   int64_t& aRangeTotal);
+                                   int64_t& aRangeTotal) const;
+
+  // Calculates the length of the resource using HTTP headers, if this
+  // is an HTTP channel. Returns -1 on failure, or for non HTTP channels.
+  int64_t CalculateStreamLength() const;
 
   struct Closure
   {
     uint32_t mLoadID;
     ChannelMediaResource* mResource;
   };
 
   static nsresult CopySegmentToCache(nsIInputStream* aInStream,

--- a/dom/media/DecoderTraits.cpp
+++ b/dom/media/DecoderTraits.cpp
@@ -320,16 +320,9 @@ bool DecoderTraits::IsSupportedInVideoDo
     ADTSDecoder::IsSupportedType(*type) ||
     FlacDecoder::IsSupportedType(*type) ||
 #ifdef MOZ_ANDROID_HLS_SUPPORT
     HLSDecoder::IsSupportedType(*type) ||
 #endif
     false;
 }
 
-/* static */
-bool
-DecoderTraits::CrossOriginRedirectsProhibited(const MediaContainerType& aType)
-{
-  return WaveDecoder::IsSupportedType(aType);
-}
-
 } // namespace mozilla

--- a/dom/media/DecoderTraits.h
+++ b/dom/media/DecoderTraits.h
@@ -52,18 +52,14 @@ public:
 
   // Returns true if aType is MIME type of hls.
   static bool IsHttpLiveStreamingType(const MediaContainerType& aType);
 
   // Returns true if aType is matroska type.
   static bool IsMatroskaType(const MediaContainerType& aType);
 
   static bool IsSupportedType(const MediaContainerType& aType);
-
-  // For some content types we block channel redirects to cross origin
-  // destinations due to security constraints. See bug 1441153.
-  static bool CrossOriginRedirectsProhibited(const MediaContainerType& aType);
 };
 
 } // namespace mozilla
 
 #endif
 

--- a/dom/media/MediaDecoderStateMachine.cpp
+++ b/dom/media/MediaDecoderStateMachine.cpp
@@ -1,33 +1,26 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* vim:set ts=2 sw=2 sts=2 et cindent: */
 /* 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/. */
 
-#ifdef XP_WIN
-// Include Windows headers required for enabling high precision timers.
-#include "windows.h"
-#include "mmsystem.h"
-#endif
-
 #include <algorithm>
 #include <stdint.h>
 
 #include "mediasink/AudioSink.h"
 #include "mediasink/AudioSinkWrapper.h"
 #include "mediasink/DecodedStream.h"
 #include "mediasink/OutputStreamManager.h"
 #include "mediasink/VideoSink.h"
 #include "mozilla/IndexSequence.h"
 #include "mozilla/Logging.h"
 #include "mozilla/MathAlgorithms.h"
 #include "mozilla/NotNull.h"
-#include "mozilla/Preferences.h"
 #include "mozilla/SharedThreadPool.h"
 #include "mozilla/Sprintf.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/TaskQueue.h"
 #include "mozilla/Tuple.h"
 #include "nsIMemoryReporter.h"
 #include "nsPrintfCString.h"
 #include "nsTArray.h"
@@ -2700,19 +2693,16 @@ MediaDecoderStateMachine::MediaDecoderSt
   INIT_MIRROR(mVolume, 1.0),
   INIT_MIRROR(mPreservesPitch, true),
   INIT_MIRROR(mLooping, false),
   INIT_MIRROR(mSameOriginMedia, false),
   INIT_MIRROR(mMediaPrincipalHandle, PRINCIPAL_HANDLE_NONE),
   INIT_CANONICAL(mDuration, NullableTimeUnit()),
   INIT_CANONICAL(mCurrentPosition, TimeUnit::Zero()),
   INIT_CANONICAL(mIsAudioDataAudible, false)
-#ifdef XP_WIN
-  , mShouldUseHiResTimers(Preferences::GetBool("media.hi-res-timers.enabled", true))
-#endif
 {
   MOZ_COUNT_CTOR(MediaDecoderStateMachine);
   NS_ASSERTION(NS_IsMainThread(), "Should be on main thread.");
 
   InitVideoQueuePrefs();
 
   DDLINKCHILD("reader", aReader);
 }
@@ -2720,20 +2710,16 @@ MediaDecoderStateMachine::MediaDecoderSt
 #undef INIT_WATCHABLE
 #undef INIT_MIRROR
 #undef INIT_CANONICAL
 
 MediaDecoderStateMachine::~MediaDecoderStateMachine()
 {
   MOZ_ASSERT(NS_IsMainThread(), "Should be on main thread.");
   MOZ_COUNT_DTOR(MediaDecoderStateMachine);
-
-#ifdef XP_WIN
-  MOZ_ASSERT(!mHiResTimersRequested);
-#endif
 }
 
 void
 MediaDecoderStateMachine::InitializationTask(MediaDecoder* aDecoder)
 {
   MOZ_ASSERT(OnTaskQueue());
 
   // Connect mirrors.
@@ -2924,22 +2910,16 @@ MediaDecoderStateMachine::StopPlayback()
   MOZ_ASSERT(OnTaskQueue());
   LOG("StopPlayback()");
 
   if (IsPlaying()) {
     mOnPlaybackEvent.Notify(MediaPlaybackEvent{
       MediaPlaybackEvent::PlaybackStopped, mPlaybackOffset });
     mMediaSink->SetPlaying(false);
     MOZ_ASSERT(!IsPlaying());
-#ifdef XP_WIN
-    if (mHiResTimersRequested) {
-      mHiResTimersRequested = false;
-      timeEndPeriod(1);
-    }
-#endif
   }
 }
 
 void MediaDecoderStateMachine::MaybeStartPlayback()
 {
   MOZ_ASSERT(OnTaskQueue());
   // Should try to start playback only after decoding first frames.
   MOZ_ASSERT(mSentFirstFrameLoadedEvent);
@@ -2952,30 +2932,16 @@ void MediaDecoderStateMachine::MaybeStar
   if (mPlayState != MediaDecoder::PLAY_STATE_PLAYING) {
     LOG("Not starting playback [mPlayState=%d]", mPlayState.Ref());
     return;
   }
 
   LOG("MaybeStartPlayback() starting playback");
   StartMediaSink();
 
-#ifdef XP_WIN
-  if (!mHiResTimersRequested && mShouldUseHiResTimers) {
-    mHiResTimersRequested = true;
-    // Ensure high precision timers are enabled on Windows, otherwise the state
-    // machine isn't woken up at reliable intervals to set the next frame, and we
-    // drop frames while painting. Note that each call must be matched by a
-    // corresponding timeEndPeriod() call. Enabling high precision timers causes
-    // the CPU to wake up more frequently on Windows 7 and earlier, which causes
-    // more CPU load and battery use. So we only enable high precision timers
-    // when we're actually playing.
-    timeBeginPeriod(1);
-  }
-#endif
-
   if (!IsPlaying()) {
     mMediaSink->SetPlaying(true);
     MOZ_ASSERT(IsPlaying());
   }
 
   mOnPlaybackEvent.Notify(
     MediaPlaybackEvent{ MediaPlaybackEvent::PlaybackStarted, mPlaybackOffset });
 }

--- a/dom/media/MediaDecoderStateMachine.h
+++ b/dom/media/MediaDecoderStateMachine.h
@@ -746,24 +746,13 @@ public:
   AbstractCanonical<media::TimeUnit>* CanonicalCurrentPosition()
   {
     return &mCurrentPosition;
   }
   AbstractCanonical<bool>* CanonicalIsAudioDataAudible()
   {
     return &mIsAudioDataAudible;
   }
-
-#ifdef XP_WIN
-  // Whether we've called timeBeginPeriod(1) to request high resolution
-  // timers. We request high resolution timers when playback starts, and
-  // turn them off when playback is paused. Enabling high resolution
-  // timers can cause higher CPU usage and battery drain on Windows 7.
-  bool mHiResTimersRequested = false;
-  // Whether we should enable high resolution timers. This is initialized at
-  // MDSM construction, and mirrors the value of media.hi-res-timers.enabled.
-  const bool mShouldUseHiResTimers;
-#endif
 };
 
 } // namespace mozilla
 
 #endif

--- a/dom/media/MediaPrefs.h
+++ b/dom/media/MediaPrefs.h
@@ -195,16 +195,17 @@ private:
 
   // resume background video decoding when the cursor is hovering over the tab.
   DECL_MEDIA_PREF("media.resume-bkgnd-video-on-tabhover",     ResumeVideoDecodingOnTabHover, bool, false);
 
   DECL_MEDIA_PREF("media.videocontrols.lock-video-orientation",  VideoOrientationLockEnabled, bool, false);
 
   // Media Seamless Looping
   DECL_MEDIA_PREF("media.seamless-looping",                   SeamlessLooping, bool, true);
+
 public:
   // Manage the singleton:
   static MediaPrefs& GetSingleton();
   static bool SingletonExists();
 
 private:
   template<class T> friend class StaticAutoPtr;
   static StaticAutoPtr<MediaPrefs> sInstance;

--- a/dom/media/mediasink/VideoSink.cpp
+++ b/dom/media/mediasink/VideoSink.cpp
@@ -1,14 +1,20 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* 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/. */
 
+#ifdef XP_WIN
+// Include Windows headers required for enabling high precision timers.
+#include "windows.h"
+#include "mmsystem.h"
+#endif
+
 #include "MediaQueue.h"
 #include "VideoSink.h"
 #include "MediaPrefs.h"
 #include "VideoUtils.h"
 
 #include "mozilla/IntegerPrintfMacros.h"
 
 namespace mozilla {
@@ -40,22 +46,29 @@ VideoSink::VideoSink(AbstractThread* aTh
   , mVideoQueue(aVideoQueue)
   , mContainer(aContainer)
   , mProducerID(ImageContainer::AllocateProducerID())
   , mFrameStats(aFrameStats)
   , mHasVideo(false)
   , mUpdateScheduler(aThread)
   , mVideoQueueSendToCompositorSize(aVQueueSentToCompositerSize)
   , mMinVideoQueueSize(MediaPrefs::RuinAvSync() ? 1 : 0)
+#ifdef XP_WIN
+  , mHiResTimersRequested(false)
+#endif
+
 {
   MOZ_ASSERT(mAudioSink, "AudioSink should exist.");
 }
 
 VideoSink::~VideoSink()
 {
+#ifdef XP_WIN
+  MOZ_ASSERT(!mHiResTimersRequested);
+#endif
 }
 
 const MediaSink::PlaybackParams&
 VideoSink::GetPlaybackParams() const
 {
   AssertOwnerThread();
 
   return mAudioSink->GetPlaybackParams();
@@ -133,16 +146,40 @@ void
 VideoSink::SetPreservesPitch(bool aPreservesPitch)
 {
   AssertOwnerThread();
 
   mAudioSink->SetPreservesPitch(aPreservesPitch);
 }
 
 void
+VideoSink::EnsureHighResTimersOnOnlyIfPlaying()
+{
+#ifdef XP_WIN
+  const bool needed = IsPlaying();
+  if (needed == mHiResTimersRequested) {
+    return;
+  }
+  if (needed) {
+    // Ensure high precision timers are enabled on Windows, otherwise the VideoSink
+    // isn't woken up at reliable intervals to set the next frame, and we
+    // drop frames while painting. Note that each call must be matched by a
+    // corresponding timeEndPeriod() call. Enabling high precision timers causes
+    // the CPU to wake up more frequently on Windows 7 and earlier, which causes
+    // more CPU load and battery use. So we only enable high precision timers
+    // when we're actually playing.
+    timeBeginPeriod(1);
+  } else {
+    timeEndPeriod(1);
+  }
+  mHiResTimersRequested = needed;
+#endif
+}
+
+void
 VideoSink::SetPlaying(bool aPlaying)
 {
   AssertOwnerThread();
   VSINK_LOG_V(" playing (%d) -> (%d)", mAudioSink->IsPlaying(), aPlaying);
 
   if (!aPlaying) {
     // Reset any update timer if paused.
     mUpdateScheduler.Reset();
@@ -156,16 +193,18 @@ VideoSink::SetPlaying(bool aPlaying)
   mAudioSink->SetPlaying(aPlaying);
 
   if (mHasVideo && aPlaying) {
     // There's no thread in VideoSink for pulling video frames, need to trigger
     // rendering while becoming playing status. because the VideoQueue may be
     // full already.
     TryUpdateRenderedVideoFrames();
   }
+
+  EnsureHighResTimersOnOnlyIfPlaying();
 }
 
 void
 VideoSink::Start(const TimeUnit& aStartTime, const MediaInfo& aInfo)
 {
   AssertOwnerThread();
   VSINK_LOG("[%s]", __func__);
 
@@ -219,16 +258,18 @@ VideoSink::Stop()
   mUpdateScheduler.Reset();
   if (mHasVideo) {
     DisconnectListener();
     mVideoSinkEndRequest.DisconnectIfExists();
     mEndPromiseHolder.ResolveIfExists(true, __func__);
     mEndPromise = nullptr;
   }
   mVideoFrameEndTime = TimeUnit::Zero();
+
+  EnsureHighResTimersOnOnlyIfPlaying();
 }
 
 bool
 VideoSink::IsStarted() const
 {
   AssertOwnerThread();
 
   return mAudioSink->IsStarted();

--- a/dom/media/mediasink/VideoSink.h
+++ b/dom/media/mediasink/VideoSink.h
@@ -74,16 +74,18 @@ private:
   virtual ~VideoSink();
 
   // VideoQueue listener related.
   void OnVideoQueuePushed(RefPtr<VideoData>&& aSample);
   void OnVideoQueueFinished();
   void ConnectListener();
   void DisconnectListener();
 
+  void EnsureHighResTimersOnOnlyIfPlaying();
+
   // Sets VideoQueue images into the VideoFrameContainer. Called on the shared
   // state machine thread. The first aMaxFrames (at most) are set.
   // aClockTime and aClockTimeStamp are used as the baseline for deriving
   // timestamps for the frames; when omitted, aMaxFrames must be 1 and
   // a null timestamp is passed to the VideoFrameContainer.
   // If the VideoQueue is empty, this does nothing.
   void RenderVideoFrames(int32_t aMaxFrames, int64_t aClockTime = 0,
                          const TimeStamp& aClickTimeStamp = TimeStamp());
@@ -146,14 +148,23 @@ private:
   // Talos tests for the compositor require at least one frame in the
   // video queue so that the compositor has something to composit during
   // the talos test when the decode is stressed. We have a minimum size
   // on the video queue in order to facilitate this talos test.
   // Note: Normal playback should not have a queue size of more than 0,
   // otherwise A/V sync will be ruined! *Only* make this non-zero for
   // testing purposes.
   const uint32_t mMinVideoQueueSize;
+
+#ifdef XP_WIN
+  // Whether we've called timeBeginPeriod(1) to request high resolution
+  // timers. We request high resolution timers when playback starts, and
+  // turn them off when playback is paused. Enabling high resolution
+  // timers can cause higher CPU usage and battery drain on Windows 7,
+  // but reduces our frame drop rate.
+  bool mHiResTimersRequested;
+#endif
 };
 
 } // namespace media
 } // namespace mozilla
 
 #endif

--- a/dom/media/test/AutoplayTestUtils.js
+++ b/dom/media/test/AutoplayTestUtils.js
@@ -11,26 +11,16 @@ function playAndPostResult(muted, parent
         parent_window.postMessage({played: true}, "*");
       },
       () => {
         parent_window.postMessage({played: false}, "*");
       }
     );
 }
 
-function nextEvent(eventTarget, eventName) {
-  return new Promise(function(resolve, reject) {
-    let f = function(event) {
-      eventTarget.removeEventListener(eventName, f, false);
-      resolve(event);
-    };
-    eventTarget.addEventListener(eventName, f, false);
-  });
-}
-
 function nextWindowMessage() {
   return nextEvent(window, "message");
 }
 
 function log(msg) {
   var log_pane = document.body;
   log_pane.appendChild(document.createTextNode(msg));
   log_pane.appendChild(document.createElement("br"));

--- a/dom/media/test/background_video.js
+++ b/dom/media/test/background_video.js
@@ -9,32 +9,16 @@
 function startTest(test) {
   info(test.desc);
   SimpleTest.waitForExplicitFinish();
   SpecialPowers.pushPrefEnv({ 'set': test.prefs }, () => {
     manager.runTests(test.tests, test.runTest);
   });
 }
 
-/**
- * @param {HTMLMediaElement} video target of interest.
- * @param {string} eventName the event to wait on.
- * @returns {Promise} A promise that is resolved when event happens.
- */
-function nextEvent(video, eventName) {
-  return new Promise(function (resolve, reject) {
-    let f = function (event) {
-      ok(true, `${video.token} ${eventName}.`);
-      video.removeEventListener(eventName, f, false);
-      resolve(event);
-    };
-    video.addEventListener(eventName, f, false);
-  });
-}
-
 function nextVideoEnded(video) {
   return nextEvent(video, 'ended');
 }
 
 function nextVideoPlaying(video) {
   return nextEvent(video, 'playing');
 }
 

deleted file mode 100644
--- a/dom/media/test/dynamic_redirect.sjs
+++ /dev/null
@@ -1,67 +0,0 @@
-function parseQuery(query, key) {
-  for (let p of query.split('&')) {
-    if (p == key) {
-      return true;
-    }
-    if (p.startsWith(key + "=")) {
-      return p.substring(key.length + 1);
-    }
-  }
-}
-
-// Return seek.ogv file content for the first request with a given key.
-// All subsequent requests return a redirect to a different-origin resource.
-function handleRequest(request, response)
-{
-  var query = request.queryString;
-  var key = parseQuery(query, "key");
-  var resource = parseQuery(query, "res");
-  var nested = parseQuery(query, "nested") || false;
-
-  dump("Received request for key = "+ key +"\n");
-  if (!nested) {
-    if (getState(key) == "redirect") {
-      var origin = request.host == "mochi.test" ? "example.org" : "mochi.test:8888";
-      response.setStatusLine(request.httpVersion, 303, "See Other");
-      let url = "http://" + origin +
-                "/tests/dom/media/test/dynamic_redirect.sjs?nested&" + query;
-      dump("Redirecting to "+ url + "\n");
-      response.setHeader("Location", url);
-      response.setHeader("Content-Type", "text/html");
-      return;
-    }
-    setState(key, "redirect");
-  }
-  var file = Components.classes["@mozilla.org/file/directory_service;1"].
-                        getService(Components.interfaces.nsIProperties).
-                        get("CurWorkD", Components.interfaces.nsIFile);
-  var fis  = Components.classes['@mozilla.org/network/file-input-stream;1'].
-                        createInstance(Components.interfaces.nsIFileInputStream);
-  var bis  = Components.classes["@mozilla.org/binaryinputstream;1"].
-                        createInstance(Components.interfaces.nsIBinaryInputStream);
-  var paths = "tests/dom/media/test/" + resource;
-  var split = paths.split("/");
-  for (var i = 0; i < split.length; ++i) {
-    file.append(split[i]);
-  }
-  fis.init(file, -1, -1, false);
-
-  bis.setInputStream(fis);
-  var bytes = bis.readBytes(bis.available());
-  let [from, to] = request.getHeader("range").split("=")[1].split("-").map(s => parseInt(s));
-  to = to || Math.max(from, bytes.length - 1);
-  byterange = bytes.substring(from, to + 1);
-
-  let contentRange = "bytes "+ from +"-"+ to +"/"+ bytes.length;
-  let contentLength = (to - from + 1).toString();
-  dump("Response Content-Range = "+ contentRange +"\n");
-  dump("Response Content-Length = "+ contentLength +"\n");
-
-  response.setStatusLine(request.httpVersion, 206, "Partial Content");
-  response.setHeader("Content-Range", contentRange);
-  response.setHeader("Content-Length", contentLength, false);
-  response.setHeader("Content-Type", "video/ogg", false);
-  response.setHeader("Accept-Ranges", "bytes", false);
-  response.write(byterange, byterange.length);
-  bis.close();
-}

--- a/dom/media/test/file_autoplay_policy_activation_frame.html
+++ b/dom/media/test/file_autoplay_policy_activation_frame.html
@@ -1,12 +1,13 @@
 <!DOCTYPE HTML>
 <html>
   <head>
     <title>Autoplay policy frame</title>
+    <script type="text/javascript" src="manifest.js"></script>
     <script type="text/javascript" src="AutoplayTestUtils.js"></script>
     <script type="text/javascript" src="/tests/SimpleTest/EventUtils.js"></script>
     <style>
       video {
         width: 50%;
         height: 50%;
       }
     </style>

new file mode 100644
--- /dev/null
+++ b/dom/media/test/file_autoplay_policy_play_before_loadedmetadata.html
@@ -0,0 +1,50 @@
+<!DOCTYPE HTML>
+<html>
+
+<head>
+  <title>Autoplay policy window</title>
+  <style>
+    video {
+      width: 50%;
+      height: 50%;
+    }
+  </style>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="/tests/SimpleTest/EventUtils.js"></script>
+  <script type="text/javascript" src="manifest.js"></script>
+  <script type="text/javascript" src="AutoplayTestUtils.js"></script>
+</head>
+
+<body>
+  <pre id="test">
+      <script>
+
+        window.is = window.opener.is;
+        window.info = window.opener.info;
+
+        async function testPlayBeforeLoadedMetata(testCase, parent_window) {
+          info("testPlayBeforeLoadedMetata: " + testCase.resource);
+
+          let element = document.createElement("video");
+          element.preload = "auto";
+          element.src = testCase.resource;
+          document.body.appendChild(element);
+
+          let played = await element.play().then(() => true, () => false);
+          let msg = testCase.resource + " should " + (!testCase.shouldPlay ? "not " : "") + "play";
+          is(played, testCase.shouldPlay, msg);
+
+          removeNodeAndSource(element);
+        }
+
+        nextWindowMessage().then(
+          async (event) => {
+            await testPlayBeforeLoadedMetata(event.data, event.source);
+            event.source.postMessage("done", "*");
+          });
+
+      </script>
+    </pre>
+</body>
+
+</html>
\ No newline at end of file

--- a/dom/media/test/manifest.js
+++ b/dom/media/test/manifest.js
@@ -1586,16 +1586,31 @@ function once(target, name, cb) {
     }, {once: true});
   });
   if (cb) {
     p.then(cb);
   }
   return p;
 }
 
+/**
+ * @param {HTMLMediaElement} video target of interest.
+ * @param {string} eventName the event to wait on.
+ * @returns {Promise} A promise that is resolved when event happens.
+ */
+function nextEvent(video, eventName) {
+  return new Promise(function (resolve, reject) {
+    let f = function (event) {
+      video.removeEventListener(eventName, f, false);
+      resolve(event);
+    };
+    video.addEventListener(eventName, f, false);
+  });
+}
+
 function TimeStamp(token) {
   function pad(x) {
     return (x < 10) ? "0" + x : x;
   }
   var now = new Date();
   var ms = now.getMilliseconds();
   var time = "[" +
              pad(now.getHours()) + ":" +

new file mode 100644
--- /dev/null
+++ b/dom/media/test/midflight-redirect.sjs
@@ -0,0 +1,78 @@
+function parseQuery(query, key) {
+  for (let p of query.split('&')) {
+    if (p == key) {
+      return true;
+    }
+    if (p.startsWith(key + "=")) {
+      return p.substring(key.length + 1);
+    }
+  }
+}
+
+// Return the first few bytes in a short byte range response. When Firefox
+// requests subsequent bytes in a second range request, respond with a
+// redirect. Requests after the first redirected are serviced as expected.
+function handleRequest(request, response)
+{
+  var query = request.queryString;
+  var resource = parseQuery(query, "resource");
+  var type = parseQuery(query, "type") || "application/octet-stream";
+  var redirected = parseQuery(query, "redirected") || false;
+  var useCors = parseQuery(query, "cors") || false;
+
+  var file = Components.classes["@mozilla.org/file/directory_service;1"].
+                        getService(Components.interfaces.nsIProperties).
+                        get("CurWorkD", Components.interfaces.nsIFile);
+  var fis  = Components.classes['@mozilla.org/network/file-input-stream;1'].
+                        createInstance(Components.interfaces.nsIFileInputStream);
+  var bis  = Components.classes["@mozilla.org/binaryinputstream;1"].
+                        createInstance(Components.interfaces.nsIBinaryInputStream);
+  var paths = "tests/dom/media/test/" + resource;
+  var split = paths.split("/");
+  for (var i = 0; i < split.length; ++i) {
+    file.append(split[i]);
+  }
+  fis.init(file, -1, -1, false);
+
+  bis.setInputStream(fis);
+  var bytes = bis.readBytes(bis.available());
+  let [from, to] = request.getHeader("range").split("=")[1].split("-").map(s => parseInt(s));
+
+  if (!redirected && from > 0) {
+    var origin = request.host == "mochi.test" ? "example.org" : "mochi.test:8888";
+    response.setStatusLine(request.httpVersion, 303, "See Other");
+    let url = "http://" + origin +
+              "/tests/dom/media/test/midflight-redirect.sjs?redirected&" + query;
+    response.setHeader("Location", url);
+    response.setHeader("Content-Type", "text/html");
+    return;
+  }
+
+  if (isNaN(to)) {
+    to = bytes.length - 1;
+  }
+
+  if (from == 0 && !redirected) {
+    to = parseInt(parseQuery(query, "redirectAt")) || Math.floor(bytes.length / 4);
+  }
+  to = Math.min(to, bytes.length - 1);
+
+  // Note: 'to' is the first index *excluded*, so we need (to + 1)
+  // in the substring end here.
+  byterange = bytes.substring(from, to + 1);
+
+  let contentRange = "bytes " + from + "-" + to + "/" + bytes.length;
+  let contentLength = byterange.length.toString();
+
+  response.setStatusLine(request.httpVersion, 206, "Partial Content");
+  response.setHeader("Content-Range", contentRange);
+  response.setHeader("Content-Length", contentLength, false);
+  response.setHeader("Content-Type", type, false);
+  response.setHeader("Accept-Ranges", "bytes", false);
+  response.setHeader("Cache-Control", "no-cache, no-store, must-revalidate");
+  if (redirected && useCors) {
+    response.setHeader("Access-Control-Allow-Origin", "*");
+  }
+  response.write(byterange, byterange.length);
+  bis.close();
+}

--- a/dom/media/test/mochitest.ini
+++ b/dom/media/test/mochitest.ini
@@ -429,23 +429,23 @@ support-files =
   detodos-short.webm
   detodos-short.webm^headers^
   detodos-recorder-test.opus
   detodos-recorder-test.opus^headers^
   detodos-short.opus
   detodos-short.opus^headers^
   dirac.ogg
   dirac.ogg^headers^
-  dynamic_redirect.sjs
   dynamic_resource.sjs
   eme.js
   file_access_controls.html
   file_autoplay_policy_unmute_pauses.html
   file_autoplay_policy_activation_window.html
   file_autoplay_policy_activation_frame.html
+  file_autoplay_policy_play_before_loadedmetadata.html
   flac-s24.flac
   flac-s24.flac^headers^
   flac-noheader-s16.flac
   flac-noheader-s16.flac^headers^
   fragment_noplay.js
   fragment_play.js
   gizmo.mp4
   gizmo.mp4^headers^
@@ -490,16 +490,17 @@ support-files =
   invalid-m2c1.opus
   invalid-m2c1.opus^headers^
   invalid-neg_discard.webm
   invalid-neg_discard.webm^headers^
   invalid-preskip.webm
   invalid-preskip.webm^headers^
   long.vtt
   manifest.js
+  midflight-redirect.sjs
   multiple-bos.ogg
   multiple-bos.ogg^headers^
   multiple-bos-more-header-fileds.ogg
   multiple-bos-more-header-fileds.ogg^headers^
   no-cues.webm
   no-cues.webm^headers^
   notags.mp3
   notags.mp3^headers^
@@ -690,16 +691,18 @@ skip-if = true # bug 475110 - disabled s
 [test_autoplay_contentEditable.html]
 skip-if = android_version == '15' || android_version == '17' || android_version == '22' # android(bug 1232305, bug 1232318, bug 1372457)
 [test_autoplay_policy.html]
 skip-if = android_version == '23' # bug 1424903
 [test_autoplay_policy_activation.html]
 skip-if = android_version == '23' # bug 1424903
 [test_autoplay_policy_unmute_pauses.html]
 skip-if = android_version == '23' # bug 1424903
+[test_autoplay_policy_play_before_loadedmetadata.html]
+skip-if = android_version == '23' # bug 1424903
 [test_buffered.html]
 skip-if = android_version == '15' || android_version == '22' # bug 1308388, android(bug 1232305)
 [test_bug448534.html]
 [test_bug463162.xhtml]
 [test_bug465498.html]
 skip-if = toolkit == 'android' # android(bug 1232305)
 [test_bug495145.html]
 skip-if = (os == 'mac' && os_version == '10.6') || (toolkit == 'android')  # bug 1311229, android(bug 1232305)
@@ -945,16 +948,17 @@ skip-if = android_version == '17' # andr
 tags=msg
 [test_mediatrack_events.html]
 skip-if = android_version == '17' # android(bug 1232305)
 [test_mediatrack_parsing_ogg.html]
 skip-if = android_version == '17' # android(bug 1232305)
 [test_mediatrack_replay_from_end.html]
 skip-if = toolkit == 'android' # android(bug 1232305)
 [test_metadata.html]
+[test_midflight_redirect_blocked.html]
 [test_mixed_principals.html]
 skip-if = toolkit == 'android' # bug 1309814, android(bug 1232305)
 [test_mozHasAudio.html]
 skip-if = toolkit == 'android' # android(bug 1232305)
 [test_multiple_mediastreamtracks.html]
 skip-if = android_version == '17' # android(bug 1232305)
 [test_networkState.html]
 skip-if = android_version == '17' # android(bug 1232305)

new file mode 100644
--- /dev/null
+++ b/dom/media/test/test_autoplay_policy_play_before_loadedmetadata.html
@@ -0,0 +1,61 @@
+<!DOCTYPE HTML>
+<html>
+
+<head>
+  <title>Autoplay policy test</title>
+  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+  <script type="text/javascript" src="manifest.js"></script>
+  <script type="text/javascript" src="AutoplayTestUtils.js"></script>
+</head>
+
+<body>
+  <pre id="test">
+      <script>
+
+        window.is = SimpleTest.is;
+        window.info = SimpleTest.info;
+
+        // Tests that videos which have no audio track will play if play()
+        // is called before the video has reached readyState >= HAVE_METADATA.
+
+        gTestPrefs.push(["media.autoplay.enabled", false],
+          ["media.autoplay.enabled.user-gestures-needed", true]);
+
+        SpecialPowers.pushPrefEnv({ 'set': gTestPrefs }, () => {
+          runTest();
+        });
+
+        let testCases = [
+          {
+            resource: "320x240.ogv", // Only video track.
+            shouldPlay: true,
+          },
+          {
+            resource: "short.mp4", // Audio and video track.
+            shouldPlay: false,
+          },
+        ];
+
+        let child_url = "file_autoplay_policy_play_before_loadedmetadata.html";
+
+        async function runTest() {
+          for (testCase of testCases) {
+            // Run each test in a new window, to ensure its user gesture
+            // activation state isn't tainted by preceeding tests.
+            let child = window.open(child_url, "", "width=500,height=500");
+            await once(child, "load");
+            child.postMessage(testCase, window.origin);
+            let result = await nextWindowMessage();
+            child.close();
+          }
+          SimpleTest.finish();
+        }
+
+        SimpleTest.waitForExplicitFinish();
+
+      </script>
+    </pre>
+</body>
+
+</html>
\ No newline at end of file