Bug 1306696 part 1 - Not show fullscreen warning when already exit fullscreen. r=dao

MozReview-Commit-ID: 7B9MA6sjv0h

--HG--
extra : rebase_source : 335d051e58f63d45d886a302a84792512bf4472b
extra : source : 2b1efcc7bc4b1ff790bdd17a1cb7d92e469e3c5c

browser/base/content/browser-fullScreenAndPointerLock.js

@@ -385,7 +385,10 @@ var FullScreen = {
         break;
       }
       case "DOMFullscreen:NewOrigin": {
-        PointerlockFsWarning.showFullScreen(aMessage.data.originNoSuffix);
+        // Don't show the warning if we've already exit fullscreen.
+        if (document.fullscreen) {
+          PointerlockFsWarning.showFullScreen(aMessage.data.originNoSuffix);
+        }
         break;
       }
       case "DOMFullscreen:Exit": {