Bug 1121671, see if using the TabSwitchDone event will work, r=test-only=change

testing/mochitest/tests/browser/browser_waitForFocus.js

@@ -23,11 +23,19 @@ function *promiseTabLoadEvent(tab, url)
 
 // Load a new blank tab
 add_task(function *() {
-  let tab = gBrowser.addTab();
+  let tab;
-  gBrowser.selectedTab = tab;
 
-  let browser = gBrowser.getBrowserForTab(tab);
+  yield new Promise(resolve => {
+    gBrowser.addEventListener("TabSwitchDone", function onSwitch() {
+      gBrowser.removeEventListener("TabSwitchDone", onSwitch);
+      executeSoon(resolve);
+    });
+    tab = gBrowser.selectedTab = gBrowser.addTab();
+  });
 
+  gURLBar.focus();
+
+  let browser = gBrowser.selectedBrowser;
   yield SimpleTest.promiseFocus(browser.contentWindowAsCPOW, true);
 
   is(document.activeElement, browser, "Browser is focused when about:blank is loaded");