Bug 1453723 - ensure we wait for the correct load, r=bgrins

Waiting for the browser to have switched remoteness before waiting for
it to load the non-about:preferences page should be enough to address this orange.

Differential Revision: https://phabricator.services.mozilla.com/D4208

--HG--
extra : moz-landing-system : lando

browser/base/content/test/urlbar/browser_urlbarAboutHomeLoading.js

@@ -16,6 +16,9 @@ add_task(async function clearURLBarAfterParentProcessURL() {
     }, {capture: true, once: true});
   });
   document.getElementById("home-button").click();
+  if (!tab.linkedBrowser.isRemoteBrowser) {
+    await BrowserTestUtils.waitForEvent(tab.linkedBrowser, "XULFrameLoaderCreated");
+  }
   await BrowserTestUtils.browserLoaded(tab.linkedBrowser);
   is(gURLBar.value, "", "URL bar should be empty");
   is(tab.linkedBrowser.userTypedValue, null, "The browser should have no recorded userTypedValue");
@@ -36,6 +39,9 @@ add_task(async function clearURLBarAfterParentProcessURLInExistingTab() {
     newTabBrowser.loadURI("about:preferences");
   });
   document.getElementById("home-button").click();
+  if (!tab.linkedBrowser.isRemoteBrowser) {
+    await BrowserTestUtils.waitForEvent(tab.linkedBrowser, "XULFrameLoaderCreated");
+  }
   await BrowserTestUtils.browserLoaded(tab.linkedBrowser);
   is(gURLBar.value, "", "URL bar should be empty");
   is(tab.linkedBrowser.userTypedValue, null, "The browser should have no recorded userTypedValue");