--- a/browser/base/content/test/general/browser_e10s_chrome_process.js
+++ b/browser/base/content/test/general/browser_e10s_chrome_process.js
@@ -117,17 +117,17 @@ let TESTS = [
   ],
 ];
 
 // The different ways to transition from one page to another
 let TRANSITIONS = [
 // Loads the new page by calling browser.loadURI directly
 function* loadURI(browser, uri) {
   info("Calling browser.loadURI");
-  browser.loadURI(uri);
+  yield BrowserTestUtils.loadURI(browser, uri);
   return true;
 },
 
 // Loads the new page by finding a link with the right href in the document and
 // clicking it
 function* clickLink(browser, uri) {
   info("Clicking link");
 

--- a/browser/base/content/test/general/browser_e10s_switchbrowser.js
+++ b/browser/base/content/test/general/browser_e10s_switchbrowser.js
@@ -192,28 +192,28 @@ add_task(function* test_synchronous() {
   let {permanentKey} = gBrowser.selectedBrowser;
   yield waitForLoad("http://example.org/" + DUMMY_PATH);
   is(gBrowser.selectedBrowser.isRemoteBrowser, expectedRemote, "Remote attribute should be correct");
   is(gBrowser.selectedBrowser.permanentKey, permanentKey, "browser.permanentKey is still the same");
 
   info("2");
   // Load another page
   info("Loading about:robots");
-  gBrowser.selectedBrowser.loadURI("about:robots");
+  yield BrowserTestUtils.loadURI(gBrowser.selectedBrowser, "about:robots");
   is(gBrowser.selectedBrowser.isRemoteBrowser, false, "Remote attribute should be correct");
   is(gBrowser.selectedBrowser.permanentKey, permanentKey, "browser.permanentKey is still the same");
 
   yield waitForDocLoadComplete();
   is(gBrowser.selectedBrowser.isRemoteBrowser, false, "Remote attribute should be correct");
   is(gBrowser.selectedBrowser.permanentKey, permanentKey, "browser.permanentKey is still the same");
 
   info("3");
   // Load the remote page again
   info("Loading http://example.org/" + DUMMY_PATH);
-  gBrowser.loadURI("http://example.org/" + DUMMY_PATH);
+  yield BrowserTestUtils.loadURI(gBrowser.selectedBrowser, "http://example.org/" + DUMMY_PATH);
   is(gBrowser.selectedBrowser.isRemoteBrowser, expectedRemote, "Remote attribute should be correct");
   is(gBrowser.selectedBrowser.permanentKey, permanentKey, "browser.permanentKey is still the same");
 
   yield waitForDocLoadComplete();
   is(gBrowser.selectedBrowser.isRemoteBrowser, expectedRemote, "Remote attribute should be correct");
   is(gBrowser.selectedBrowser.permanentKey, permanentKey, "browser.permanentKey is still the same");
 
   info("4");

--- a/browser/base/content/test/general/browser_testOpenNewRemoteTabsFromNonRemoteBrowsers.js
+++ b/browser/base/content/test/general/browser_testOpenNewRemoteTabsFromNonRemoteBrowsers.js
@@ -21,17 +21,17 @@ function frame_script() {
 /**
  * Takes some browser in some window, and forces that browser
  * to become non-remote, and then navigates it to a page that
  * we're not supposed to be displaying remotely. Returns a
  * Promise that resolves when the browser is no longer remote.
  */
 function prepareNonRemoteBrowser(aWindow, browser) {
   browser.loadURI(NON_REMOTE_PAGE);
-  return waitForDocLoadComplete(browser);
+  return BrowserTestUtils.browserLoaded(browser);
 }
 
 registerCleanupFunction(() => {
   Services.prefs.clearUserPref(OPEN_LOCATION_PREF);
 });
 
 /**
  * Test that if we open a new tab from a link in a non-remote

--- a/browser/components/customizableui/test/browser_934951_zoom_in_toolbar.js
+++ b/browser/components/customizableui/test/browser_934951_zoom_in_toolbar.js
@@ -5,17 +5,19 @@
 "use strict";
 
 const kTimeoutInMS = 20000;
 
 // Bug 934951 - Zoom controls percentage label doesn't update when it's in the toolbar and you navigate.
 add_task(function() {
   CustomizableUI.addWidgetToArea("zoom-controls", CustomizableUI.AREA_NAVBAR);
   let tab1 = gBrowser.addTab("about:mozilla");
-  let tab2 = gBrowser.addTab("about:newtab");
+  yield BrowserTestUtils.browserLoaded(tab1.linkedBrowser);
+  let tab2 = gBrowser.addTab("about:robots");
+  yield BrowserTestUtils.browserLoaded(tab2.linkedBrowser);
   gBrowser.selectedTab = tab1;
   let zoomResetButton = document.getElementById("zoom-reset-button");
 
   registerCleanupFunction(() => {
     info("Cleaning up.");
     CustomizableUI.reset();
     gBrowser.removeTab(tab2);
     gBrowser.removeTab(tab1);
@@ -25,17 +27,17 @@ add_task(function() {
   let zoomChangePromise = promiseObserverNotification("browser-fullZoom:zoomChange");
   FullZoom.enlarge();
   yield zoomChangePromise;
   is(parseInt(zoomResetButton.label, 10), 110, "Zoom is changed to 110% for about:mozilla");
 
   let tabSelectPromise = promiseTabSelect();
   gBrowser.selectedTab = tab2;
   yield tabSelectPromise;
-  is(parseInt(zoomResetButton.label, 10), 100, "Default zoom is 100% for about:newtab");
+  is(parseInt(zoomResetButton.label, 10), 100, "Default zoom is 100% for about:robots");
 
   gBrowser.selectedTab = tab1;
   let zoomResetPromise = promiseObserverNotification("browser-fullZoom:zoomReset");
   FullZoom.reset();
   yield zoomResetPromise;
   is(parseInt(zoomResetButton.label, 10), 100, "Default zoom is 100% for about:mozilla");
 
   // Test zoom label updates while navigating pages in the same tab.
@@ -47,16 +49,17 @@ add_task(function() {
   });
   yield promiseTabLoadEvent(tab1, "about:home");
   yield attributeChangePromise;
   is(parseInt(zoomResetButton.label, 10), 100, "Default zoom is 100% for about:home");
   yield promiseTabHistoryNavigation(-1, function() {
     return parseInt(zoomResetButton.label, 10) == 110;
   });
   is(parseInt(zoomResetButton.label, 10), 110, "Zoom is still 110% for about:mozilla");
+  FullZoom.reset();
 });
 
 function promiseObserverNotification(aObserver) {
   let deferred = Promise.defer();
   function notificationCallback(e) {
     Services.obs.removeObserver(notificationCallback, aObserver, false);
     clearTimeout(timeoutId);
     deferred.resolve();

--- a/browser/components/sessionstore/test/browser_async_remove_tab.js
+++ b/browser/components/sessionstore/test/browser_async_remove_tab.js
@@ -157,17 +157,17 @@ add_task(function* save_worthy_tabs_remo
 });
 
 add_task(function* save_worthy_tabs_nonremote_final() {
   let {tab, r} = yield createTabWithRandomValue("about:blank");
   let browser = tab.linkedBrowser;
   ok(browser.isRemoteBrowser, "browser is remote");
 
   // Replace about:blank with a non-remote entry.
-  browser.loadURI("about:robots");
+  yield BrowserTestUtils.loadURI(browser, "about:robots");
   ok(!browser.isRemoteBrowser, "browser is not remote anymore");
 
   // Wait until the new entry replaces about:blank.
   yield promiseHistoryEntryReplacedNonRemote(browser);
 
   // Remove the tab before the update arrives.
   let promise = promiseRemoveTab(tab);
 

--- a/browser/components/sessionstore/test/browser_sessionHistory.js
+++ b/browser/components/sessionstore/test/browser_sessionHistory.js
@@ -7,18 +7,20 @@
  * Ensure that starting a load invalidates shistory.
  */
 add_task(function test_load_start() {
   // Create a new tab.
   let tab = gBrowser.addTab("about:blank");
   let browser = tab.linkedBrowser;
   yield promiseBrowserLoaded(browser);
 
-  // Load a new URI but remove the tab before it has finished loading.
-  browser.loadURI("about:mozilla");
+  // Load a new URI.
+  yield BrowserTestUtils.loadURI(browser, "about:mozilla");
+
+  // Remove the tab before it has finished loading.
   yield promiseContentMessage(browser, "ss-test:OnHistoryReplaceEntry");
   yield promiseRemoveTab(tab);
 
   // Undo close the tab.
   tab = ss.undoCloseTab(window, 0);
   browser = tab.linkedBrowser;
   yield promiseTabRestored(tab);
 

--- a/browser/components/sessionstore/test/head.js
+++ b/browser/components/sessionstore/test/head.js
@@ -423,18 +423,31 @@ function whenNewWindowLoaded(aOptions, a
   let url = "about:blank";
 
   if (aOptions && aOptions.private || false) {
     features = ",private";
     url = "about:privatebrowsing";
   }
 
   let win = openDialog(getBrowserURL(), "", "chrome,all,dialog=no" + features, url);
-  whenDelayedStartupFinished(win, () => aCallback(win));
-  return win;
+  let delayedStartup = promiseDelayedStartupFinished(win);
+
+  let browserLoaded = new Promise(resolve => {
+    if (url == "about:blank") {
+      resolve();
+      return;
+    }
+
+    win.addEventListener("load", function onLoad() {
+      win.removeEventListener("load", onLoad);
+      resolve(promiseBrowserLoaded(win.gBrowser.selectedBrowser));
+    });
+  });
+
+  Promise.all([delayedStartup, browserLoaded]).then(() => aCallback(win));
 }
 function promiseNewWindowLoaded(aOptions) {
   return new Promise(resolve => whenNewWindowLoaded(aOptions, resolve));
 }
 
 /**
  * Chrome windows aren't closed synchronously. Provide a helper method to close
  * a window and wait until we received the "domwindowclosed" notification for it.

--- a/netwerk/test/browser/browser_child_resource.js
+++ b/netwerk/test/browser/browser_child_resource.js
@@ -133,17 +133,17 @@ let restart = Task.async(function*() {
   if (browser.getAttribute("remote") != "true")
     return browser;
 
   browser.messageManager.sendAsyncMessage("Test:Crash");
   yield waitForEvent(browser, "AboutTabCrashedLoad", false, true);
 
   browser.reload();
 
-  yield waitForEvent(browser, "load", true);
+  yield BrowserTestUtils.browserLoaded(browser);
   is(browser.getAttribute("remote"), expectedRemote, "Browser should be in the right process");
   browser.messageManager.loadFrameScript("data:,(" + frameScript.toString() + ")();", true);
   return browser;
 });
 
 // Sanity check that this test is going to be useful
 add_task(function*() {
   let browser = yield loadTestTab();

--- a/testing/mochitest/BrowserTestUtils/BrowserTestUtils.jsm
+++ b/testing/mochitest/BrowserTestUtils/BrowserTestUtils.jsm
@@ -23,16 +23,19 @@ Cu.import("resource://gre/modules/Task.j
 Cu.import("resource://gre/modules/Timer.jsm");
 Cu.import("resource://testing-common/TestUtils.jsm");
 
 Cc["@mozilla.org/globalmessagemanager;1"]
   .getService(Ci.nsIMessageListenerManager)
   .loadFrameScript(
     "chrome://mochikit/content/tests/BrowserTestUtils/content-utils.js", true);
 
+XPCOMUtils.defineLazyModuleGetter(this, "E10SUtils",
+  "resource:///modules/E10SUtils.jsm");
+
 this.BrowserTestUtils = {
   /**
    * Loads a page in a new tab, executes a Task and closes the tab.
    *
    * @param options
    *        An object with the following properties:
    *        {
    *          gBrowser:
@@ -146,16 +149,50 @@ this.BrowserTestUtils = {
           mm.removeMessageListener("browser-test-utils:loadEvent", onLoad);
           resolve();
         }
       });
     });
   },
 
   /**
+   * Loads a new URI in the given browser and waits until we really started
+   * loading. In e10s browser.loadURI() can be an asynchronous operation due
+   * to having to switch the browser's remoteness and keep its shistory data.
+   *
+   * @param {xul:browser} browser
+   *        A xul:browser.
+   * @param {string} uri
+   *        The URI to load.
+   *
+   * @return {Promise}
+   * @resolves When we started loading the given URI.
+   */
+  loadURI: Task.async(function* (browser, uri) {
+    // Load the new URI.
+    browser.loadURI(uri);
+
+    // Nothing to do in non-e10s mode.
+    if (!browser.ownerDocument.defaultView.gMultiProcessBrowser) {
+      return;
+    }
+
+    // Retrieve the given browser's current process type.
+    let process = browser.isRemoteBrowser ? Ci.nsIXULRuntime.PROCESS_TYPE_CONTENT
+                                          : Ci.nsIXULRuntime.PROCESS_TYPE_DEFAULT;
+
+    // If the new URI can't load in the browser's current process then we
+    // should wait for the new frameLoader to be created. This will happen
+    // asynchronously when the browser's remoteness changes.
+    if (!E10SUtils.canLoadURIInProcess(uri, process)) {
+      yield this.waitForEvent(browser, "XULFrameLoaderCreated");
+    }
+  }),
+
+  /**
    * @return {Promise}
    *         A Promise which resolves when a "domwindowopened" notification
    *         has been fired by the window watcher.
    */
   domWindowOpened() {
     return new Promise(resolve => {
       function observer(subject, topic, data) {
         if (topic != "domwindowopened") { return; }