Issue 3697 - Fall back to i18n.getUILanguage if @ui_locale isn't supported

lib/notificationHelper.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 194 matching lines @@
     }
     else if ("Notification" in window && activeNotification.type != "question")
     {
       if (linkCount > 0)
         message += " " + ext.i18n.getMessage("notification_without_buttons");
 
       let notification = new Notification(
         title,
         {
           lang: Utils.appLocale,
-          dir: ext.i18n.getMessage("@@bidi_dir"),
+          dir: Utils.readingDirection,
           body: message,
           icon: iconUrl
         }
       );
 
       notification.addEventListener("click", openNotificationLinks);
       notification.addEventListener("close", notificationClosed);
     }
     else
     {
@@ skipping 45 matching lines @@
   let methods = displayMethods[notificationType] || defaultDisplayMethods;
   return methods.indexOf(method) > -1;
 };
 
 ext.pages.onLoading.addListener(page =>
 {
   NotificationStorage.showNext(stringifyURL(page.url));
 });
 
 NotificationStorage.addShowListener(showNotification);