--- a/browser/base/content/test/general/browser_tab_dragdrop.js
+++ b/browser/base/content/test/general/browser_tab_dragdrop.js
@@ -1,131 +1,117 @@
-function test()
-{
-  var embed = '<embed type="application/x-test" allowscriptaccess="always" allowfullscreen="true" wmode="window" width="640" height="480"></embed>'
+function swapTabsAndCloseOther(a, b) {
+  gBrowser.swapBrowsersAndCloseOther(gBrowser.tabs[b], gBrowser.tabs[a]);
+}
+
+let getClicks = function(tab) {
+  return ContentTask.spawn(tab.linkedBrowser, {}, function() {
+    return content.wrappedJSObject.clicks;
+  });
+}
+
+let clickTest = Task.async(function*(tab) {
+  let clicks = yield getClicks(tab);
 
-  waitForExplicitFinish();
+  yield ContentTask.spawn(tab.linkedBrowser, {}, function() {
+    let target = content.document.body;
+    let rect = target.getBoundingClientRect();
+    let left = (rect.left + rect.right) / 2;
+    let top = (rect.top + rect.bottom) / 2;
+
+    let utils = content.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
+                       .getInterface(Components.interfaces.nsIDOMWindowUtils);
+    utils.sendMouseEvent("mousedown", left, top, 0, 1, 0, false, 0, 0);
+    utils.sendMouseEvent("mouseup", left, top, 0, 1, 0, false, 0, 0);
+  });
+
+  let newClicks = yield getClicks(tab);
+  is(newClicks, clicks + 1, "adding 1 more click on BODY");
+});
+
+function loadURI(tab, url) {
+  tab.linkedBrowser.loadURI(url);
+  return BrowserTestUtils.browserLoaded(tab.linkedBrowser);
+}
+
+add_task(function*() {
+  let embed = '<embed type="application/x-test" allowscriptaccess="always" allowfullscreen="true" wmode="window" width="640" height="480"></embed>'
   setTestPluginEnabledState(Ci.nsIPluginTag.STATE_ENABLED);
 
   // create a few tabs
-  var tabs = [
+  let tabs = [
     gBrowser.tabs[0],
     gBrowser.addTab("about:blank", {skipAnimation: true}),
     gBrowser.addTab("about:blank", {skipAnimation: true}),
     gBrowser.addTab("about:blank", {skipAnimation: true}),
     gBrowser.addTab("about:blank", {skipAnimation: true})
   ];
 
-  function setLocation(i, url) {
-    tabs[i].linkedBrowser.contentWindow.location = url;
-  }
-  function moveTabTo(a, b) {
-    gBrowser.swapBrowsersAndCloseOther(gBrowser.tabs[b], gBrowser.tabs[a]);
-  }
-  function clickTest(tab, doc, win) {
-    var clicks = doc.defaultView.clicks;
-
-    yield ContentTask.spawn(tab.linkedBrowser, {}, function() {
-      let target = content.document.body;
-      let rect = target.getBoundingClientRect();
-      let left = (rect.left + rect.right) / 2;
-      let top = (rect.top + rect.bottom) / 2;
-
-      let utils = content.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
-                         .getInterface(Components.interfaces.nsIDOMWindowUtils);
-      utils.sendMouseEvent("mousedown", left, top, 0, 1, 0, false, 0, 0);
-      utils.sendMouseEvent("mouseup", left, top, 0, 1, 0, false, 0, 0);
-    });
-
-    is(doc.defaultView.clicks, clicks+1, "adding 1 more click on BODY");
-  }
-  function test1() {
-    moveTabTo(2, 3); // now: 0 1 2 4
-    is(gBrowser.tabs[1], tabs[1], "tab1");
-    is(gBrowser.tabs[2], tabs[3], "tab3");
-
-    var plugin = tabs[4].linkedBrowser.contentDocument.wrappedJSObject.body.firstChild;
-    var tab4_plugin_object = plugin.getObjectValue();
-
-    gBrowser.selectedTab = gBrowser.tabs[2];
-    moveTabTo(3, 2); // now: 0 1 4
-    gBrowser.selectedTab = tabs[4];
-    var doc = gBrowser.tabs[2].linkedBrowser.contentDocument.wrappedJSObject;
-    plugin = doc.body.firstChild;
-    ok(plugin && plugin.checkObjectValue(tab4_plugin_object), "same plugin instance");
-    is(gBrowser.tabs[1], tabs[1], "tab1");
-    is(gBrowser.tabs[2], tabs[3], "tab4");
-    is(doc.defaultView.clicks, 0, "no click on BODY so far");
-    clickTest(gBrowser.tabs[2], doc, window);
-
-    moveTabTo(2, 1); // now: 0 4
-    is(gBrowser.tabs[1], tabs[1], "tab1");
-    doc = gBrowser.tabs[1].linkedBrowser.contentDocument.wrappedJSObject;
-    plugin = doc.body.firstChild;
-    ok(plugin && plugin.checkObjectValue(tab4_plugin_object), "same plugin instance");
-    clickTest(gBrowser.tabs[1], doc, window);
-
-    // Load a new document (about:blank) in tab4, then detach that tab into a new window.
-    // In the new window, navigate back to the original document and click on its <body>,
-    // verify that its onclick was called.
-    var t = tabs[1];
-    var b = t.linkedBrowser;
-    gBrowser.selectedTab = t;
-    b.addEventListener("load", function() {
-      b.removeEventListener("load", arguments.callee, true);
-
-      executeSoon(function () {
-        var win = gBrowser.replaceTabWithWindow(t);
-        whenDelayedStartupFinished(win, function () {
-          // Verify that the original window now only has the initial tab left in it.
-          is(gBrowser.tabs[0], tabs[0], "tab0");
-          is(gBrowser.tabs[0].linkedBrowser.contentWindow.location, "about:blank", "tab0 uri");
-
-          executeSoon(function () {
-            win.gBrowser.addEventListener("pageshow", function () {
-              win.gBrowser.removeEventListener("pageshow", arguments.callee, false);
-              executeSoon(function () {
-                t = win.gBrowser.tabs[0];
-                b = t.linkedBrowser;
-                var doc = b.contentDocument.wrappedJSObject;
-                clickTest(t, doc, win);
-                win.close();
-                finish();
-              });
-            }, false);
-            win.gBrowser.goBack();
-          });
-        });
-      });
-    }, true);
-    b.loadURI("about:blank");
-
-  }
-
-  var loads = 0;
-  function waitForLoad(event, tab, listenerContainer) {
-    var b = tabs[tab].linkedBrowser;
-    if (b.contentDocument != event.target) {
-      return;
-    }
-    gBrowser.tabs[tab].linkedBrowser.removeEventListener("load", listenerContainer.listener, true);
-    ++loads;
-    if (loads == tabs.length - 1) {
-      executeSoon(test1);
-    }
-  }
-
-  function fn(f, arg) {
-    var listenerContainer = { listener: null }
-    listenerContainer.listener = function (event) { return f(event, arg, listenerContainer); };
-    return listenerContainer.listener;
-  }
-  for (var i = 1; i < tabs.length; ++i) {
-    tabs[i].linkedBrowser.addEventListener("load", fn(waitForLoad,i), true);
-  }
-
-  setLocation(1, "data:text/html;charset=utf-8,<title>tab1</title><body>tab1<iframe>");
-  setLocation(2, "data:text/plain;charset=utf-8,tab2");
-  setLocation(3, "data:text/html;charset=utf-8,<title>tab3</title><body>tab3<iframe>");
-  setLocation(4, "data:text/html;charset=utf-8,<body onload='clicks=0' onclick='++clicks'>"+embed);
+  // Initially 0 1 2 3 4
+  yield loadURI(tabs[1], "data:text/html;charset=utf-8,<title>tab1</title><body>tab1<iframe>");
+  yield loadURI(tabs[2], "data:text/plain;charset=utf-8,tab2");
+  yield loadURI(tabs[3], "data:text/html;charset=utf-8,<title>tab3</title><body>tab3<iframe>");
+  yield loadURI(tabs[4], "data:text/html;charset=utf-8,<body onload='clicks=0' onclick='++clicks'>"+embed);
   gBrowser.selectedTab = tabs[3];
 
-}
+  swapTabsAndCloseOther(2, 3); // now: 0 1 2 4
+  is(gBrowser.tabs[1], tabs[1], "tab1");
+  is(gBrowser.tabs[2], tabs[3], "tab3");
+  is(gBrowser.tabs[3], tabs[4], "tab4");
+
+  let plugin = tabs[4].linkedBrowser.contentDocument.wrappedJSObject.body.firstChild;
+  let tab4_plugin_object = plugin.getObjectValue();
+
+  swapTabsAndCloseOther(3, 2); // now: 0 1 4
+  gBrowser.selectedTab = gBrowser.tabs[2];
+
+  let doc = gBrowser.tabs[2].linkedBrowser.contentDocument.wrappedJSObject;
+  plugin = doc.body.firstChild;
+  ok(plugin && plugin.checkObjectValue(tab4_plugin_object), "same plugin instance");
+
+  is(gBrowser.tabs[1], tabs[1], "tab1");
+  is(gBrowser.tabs[2], tabs[3], "tab4");
+
+  let clicks = yield getClicks(gBrowser.tabs[2]);
+  is(clicks, 0, "no click on BODY so far");
+  yield clickTest(gBrowser.tabs[2]);
+
+  swapTabsAndCloseOther(2, 1); // now: 0 4
+  is(gBrowser.tabs[1], tabs[1], "tab1");
+
+  doc = gBrowser.tabs[1].linkedBrowser.contentDocument.wrappedJSObject;
+  plugin = doc.body.firstChild;
+  ok(plugin && plugin.checkObjectValue(tab4_plugin_object), "same plugin instance");
+
+  yield clickTest(gBrowser.tabs[1]);
+
+  // Load a new document (about:blank) in tab4, then detach that tab into a new window.
+  // In the new window, navigate back to the original document and click on its <body>,
+  // verify that its onclick was called.
+  gBrowser.selectedTab = tabs[1];
+  yield loadURI(tabs[1], "about:blank");
+  let key = tabs[1].linkedBrowser.permanentKey;
+
+  let win = gBrowser.replaceTabWithWindow(tabs[1]);
+  yield new Promise(resolve => whenDelayedStartupFinished(win, resolve));
+
+  // Verify that the original window now only has the initial tab left in it.
+  is(gBrowser.tabs[0], tabs[0], "tab0");
+  is(gBrowser.tabs[0].linkedBrowser.currentURI.spec, "about:blank", "tab0 uri");
+
+  let tab = win.gBrowser.tabs[0];
+  is(tab.linkedBrowser.permanentKey, key, "Should have kept the key");
+
+  let pageshowPromise = ContentTask.spawn(tab.linkedBrowser, {}, function*() {
+    return new Promise(resolve => {
+      let listener = function() {
+        removeEventListener("pageshow", listener, false);
+        resolve();
+      }
+      addEventListener("pageshow", listener, false);
+    });
+  });
+  win.gBrowser.goBack();
+  yield pageshowPromise;
+
+  yield clickTest(tab);
+  promiseWindowClosed(win);
+});

--- a/browser/base/content/test/general/browser_tabopen_reflows.js
+++ b/browser/base/content/test/general/browser_tabopen_reflows.js
@@ -50,18 +50,17 @@ const EXPECTED_REFLOWS = [
 
 const PREF_PRELOAD = "browser.newtab.preload";
 const PREF_NEWTAB_DIRECTORYSOURCE = "browser.newtabpage.directory.source";
 
 /*
  * This test ensures that there are no unexpected
  * uninterruptible reflows when opening new tabs.
  */
-function test() {
-  waitForExplicitFinish();
+add_task(function*() {
   let DirectoryLinksProvider = Cu.import("resource:///modules/DirectoryLinksProvider.jsm", {}).DirectoryLinksProvider;
   let NewTabUtils = Cu.import("resource://gre/modules/NewTabUtils.jsm", {}).NewTabUtils;
   let Promise = Cu.import("resource://gre/modules/Promise.jsm", {}).Promise;
 
   // resolves promise when directory links are downloaded and written to disk
   function watchLinksChangeOnce() {
     let deferred = Promise.defer();
     let observer = {
@@ -80,35 +79,46 @@ function test() {
 
   let gOrigDirectorySource = Services.prefs.getCharPref(PREF_NEWTAB_DIRECTORYSOURCE);
   registerCleanupFunction(() => {
     Services.prefs.clearUserPref(PREF_PRELOAD);
     Services.prefs.setCharPref(PREF_NEWTAB_DIRECTORYSOURCE, gOrigDirectorySource);
     return watchLinksChangeOnce();
   });
 
-  // run tests when directory source change completes
-  watchLinksChangeOnce().then(() => {
-    // Add a reflow observer and open a new tab.
-    docShell.addWeakReflowObserver(observer);
-    BrowserOpenTab();
-
-    // Wait until the tabopen animation has finished.
-    waitForTransitionEnd(function () {
-      // Remove reflow observer and clean up.
-      docShell.removeWeakReflowObserver(observer);
-      gBrowser.removeCurrentTab();
-      finish();
-    });
-  });
-
   Services.prefs.setBoolPref(PREF_PRELOAD, false);
   // set directory source to dummy/empty links
   Services.prefs.setCharPref(PREF_NEWTAB_DIRECTORYSOURCE, 'data:application/json,{"test":1}');
-}
+
+  // run tests when directory source change completes
+  yield watchLinksChangeOnce();
+
+  // Perform a click in the top left of content to ensure the mouse isn't
+  // hovering over any of the tiles
+  let target = gBrowser.selectedBrowser;
+  let rect = target.getBoundingClientRect();
+  let left = rect.left + 1;
+  let top = rect.top + 1;
+
+  let utils = window.QueryInterface(Ci.nsIInterfaceRequestor)
+                    .getInterface(Ci.nsIDOMWindowUtils);
+  utils.sendMouseEvent("mousedown", left, top, 0, 1, 0, false, 0, 0);
+  utils.sendMouseEvent("mouseup", left, top, 0, 1, 0, false, 0, 0);
+
+  // Add a reflow observer and open a new tab.
+  docShell.addWeakReflowObserver(observer);
+  BrowserOpenTab();
+
+  // Wait until the tabopen animation has finished.
+  yield waitForTransitionEnd();
+
+  // Remove reflow observer and clean up.
+  docShell.removeWeakReflowObserver(observer);
+  gBrowser.removeCurrentTab();
+});
 
 let observer = {
   reflow: function (start, end) {
     // Gather information about the current code path.
     let path = (new Error().stack).split("\n").slice(1).map(line => {
       return line.replace(/:\d+:\d+$/, "");
     }).join("|");
     let pathWithLineNumbers = (new Error().stack).split("\n").slice(1).join("|");
@@ -132,17 +142,19 @@ let observer = {
   reflowInterruptible: function (start, end) {
     // We're not interested in interruptible reflows.
   },
 
   QueryInterface: XPCOMUtils.generateQI([Ci.nsIReflowObserver,
                                          Ci.nsISupportsWeakReference])
 };
 
-function waitForTransitionEnd(callback) {
-  let tab = gBrowser.selectedTab;
-  tab.addEventListener("transitionend", function onEnd(event) {
-    if (event.propertyName === "max-width") {
-      tab.removeEventListener("transitionend", onEnd);
-      executeSoon(callback);
-    }
+function waitForTransitionEnd() {
+  return new Promise(resolve => {
+    let tab = gBrowser.selectedTab;
+    tab.addEventListener("transitionend", function onEnd(event) {
+      if (event.propertyName === "max-width") {
+        tab.removeEventListener("transitionend", onEnd);
+        resolve();
+      }
+    });
   });
 }

--- a/testing/mochitest/BrowserTestUtils/ContentTask.jsm
+++ b/testing/mochitest/BrowserTestUtils/ContentTask.jsm
@@ -5,17 +5,17 @@
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 "use strict";
 
 this.EXPORTED_SYMBOLS = [
   "ContentTask"
 ];
 
-const Cu = Components.utils;
+const { classes: Cc, interfaces: Ci, utils: Cu } = Components;
 Cu.import("resource://gre/modules/Promise.jsm");
 
 /**
  * Set of browsers which have loaded the content-task frame script.
  */
 let gScriptLoadedSet = new WeakSet();
 
 /**
@@ -45,23 +45,22 @@ this.ContentTask = {
    *          sent to the remote browser.
    * @return A promise object where you can register completion callbacks to be
    *         called when the task terminates.
    * @resolves With the final returned value of the task if it executes
    *           successfully.
    * @rejects An error message if execution fails.
    */
   spawn: function ContentTask_spawn(browser, arg, task) {
-    if(!gScriptLoadedSet.has(browser)) {
+    if(!gScriptLoadedSet.has(browser.permanentKey)) {
       let mm = browser.messageManager;
-      mm.addMessageListener("content-task:complete", ContentMessageListener);
       mm.loadFrameScript(
         "chrome://mochikit/content/tests/BrowserTestUtils/content-task.js", true);
 
-      gScriptLoadedSet.add(browser);
+      gScriptLoadedSet.add(browser.permanentKey);
     }
 
     let deferred = {};
     deferred.promise = new Promise((resolve, reject) => {
       deferred.resolve = resolve;
       deferred.reject = reject;
     });
 
@@ -88,8 +87,10 @@ let ContentMessageListener = {
 
     if (aMessage.data.error) {
       deferred.reject(aMessage.data.error);
     } else {
       deferred.resolve(aMessage.data.result);
     }
   },
 };
+Cc["@mozilla.org/globalmessagemanager;1"].getService(Ci.nsIMessageListenerManager)
+  .addMessageListener("content-task:complete", ContentMessageListener);