diff --git a/browser/base/content/test/general/browser_e10s_chrome_process.js b/browser/base/content/test/general/browser_e10s_chrome_process.js
index 64187d3b291..858cfd8fba9 100644
--- a/browser/base/content/test/general/browser_e10s_chrome_process.js
+++ b/browser/base/content/test/general/browser_e10s_chrome_process.js
@@ -122,7 +122,7 @@ 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;
 },
 
diff --git a/browser/base/content/test/general/browser_e10s_switchbrowser.js b/browser/base/content/test/general/browser_e10s_switchbrowser.js
index cb13411faa4..e88d2fbcbba 100644
--- a/browser/base/content/test/general/browser_e10s_switchbrowser.js
+++ b/browser/base/content/test/general/browser_e10s_switchbrowser.js
@@ -197,7 +197,7 @@ add_task(function* test_synchronous() {
   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");
 
@@ -208,7 +208,7 @@ add_task(function* test_synchronous() {
   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");
 
diff --git a/browser/base/content/test/general/browser_testOpenNewRemoteTabsFromNonRemoteBrowsers.js b/browser/base/content/test/general/browser_testOpenNewRemoteTabsFromNonRemoteBrowsers.js
index 2c3b5a43cc8..30e1eb98b7b 100644
--- a/browser/base/content/test/general/browser_testOpenNewRemoteTabsFromNonRemoteBrowsers.js
+++ b/browser/base/content/test/general/browser_testOpenNewRemoteTabsFromNonRemoteBrowsers.js
@@ -26,7 +26,7 @@ function frame_script() {
  */
 function prepareNonRemoteBrowser(aWindow, browser) {
   browser.loadURI(NON_REMOTE_PAGE);
-  return waitForDocLoadComplete(browser);
+  return BrowserTestUtils.browserLoaded(browser);
 }
 
 registerCleanupFunction(() => {
diff --git a/browser/components/customizableui/test/browser_934951_zoom_in_toolbar.js b/browser/components/customizableui/test/browser_934951_zoom_in_toolbar.js
index 6eea69c8962..151e1cada77 100644
--- a/browser/components/customizableui/test/browser_934951_zoom_in_toolbar.js
+++ b/browser/components/customizableui/test/browser_934951_zoom_in_toolbar.js
@@ -10,7 +10,9 @@ const kTimeoutInMS = 20000;
 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");
 
@@ -30,7 +32,7 @@ add_task(function() {
   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");
@@ -52,6 +54,7 @@ add_task(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) {
diff --git a/browser/components/sessionstore/test/browser_async_remove_tab.js b/browser/components/sessionstore/test/browser_async_remove_tab.js
index 1628dd02f4d..20f3463d040 100644
--- a/browser/components/sessionstore/test/browser_async_remove_tab.js
+++ b/browser/components/sessionstore/test/browser_async_remove_tab.js
@@ -162,7 +162,7 @@ add_task(function* save_worthy_tabs_nonremote_final() {
   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.
diff --git a/browser/components/sessionstore/test/browser_sessionHistory.js b/browser/components/sessionstore/test/browser_sessionHistory.js
index 95240838981..6e5a89878d3 100644
--- a/browser/components/sessionstore/test/browser_sessionHistory.js
+++ b/browser/components/sessionstore/test/browser_sessionHistory.js
@@ -12,8 +12,10 @@ add_task(function test_load_start() {
   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);
 
diff --git a/browser/components/sessionstore/test/head.js b/browser/components/sessionstore/test/head.js
index 9519cc27244..326cf92a70b 100644
--- a/browser/components/sessionstore/test/head.js
+++ b/browser/components/sessionstore/test/head.js
@@ -428,8 +428,21 @@ function whenNewWindowLoaded(aOptions, aCallback) {
   }
 
   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));
diff --git a/netwerk/test/browser/browser_child_resource.js b/netwerk/test/browser/browser_child_resource.js
index c63fb17589c..0e5ae9e611b 100644
--- a/netwerk/test/browser/browser_child_resource.js
+++ b/netwerk/test/browser/browser_child_resource.js
@@ -138,7 +138,7 @@ let restart = Task.async(function*() {
 
   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;
diff --git a/testing/mochitest/BrowserTestUtils/BrowserTestUtils.jsm b/testing/mochitest/BrowserTestUtils/BrowserTestUtils.jsm
index 21dd4703068..80d3a681096 100644
--- a/testing/mochitest/BrowserTestUtils/BrowserTestUtils.jsm
+++ b/testing/mochitest/BrowserTestUtils/BrowserTestUtils.jsm
@@ -28,6 +28,9 @@ Cc["@mozilla.org/globalmessagemanager;1"]
   .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.
@@ -150,6 +153,40 @@ this.BrowserTestUtils = {
     });
   },
 
+  /**
+   * 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