Bug 753273 - Wait for window and browser at the start of newSession, r=mdas, a=test-only, DONTBUILD because NPOTB

testing/marionette/marionette-actors.js

@@ -336,8 +336,21 @@ MarionetteDriverActor.prototype = {
    *
    */
   newSession: function MDA_newSession() {
+
+    function waitForWindow() {
+      let checkTimer = Cc["@mozilla.org/timer;1"].
+                       createInstance(Ci.nsITimer);
+      let win = this.getCurrentWindow();
+      if (!win || (appName != "B2G" && !win.gBrowser)) { 
+        checkTimer.initWithCallback(waitForWindow.bind(this), 100, Ci.nsITimer.TYPE_ONE_SHOT);
+      }
+      else {
+        this.startBrowser(win, true);
+      }
+    }
+
     if (!prefs.getBoolPref("marionette.contentListener")) {
-      this.startBrowser(this.getCurrentWindow(), true);
+      waitForWindow.call(this);
     }
     else if ((appName == "B2G") && (this.curBrowser == null)) {
       //if there is a content listener, then we just wake it up