Issue 4795 - Use modern JavaScript syntax

utils.js

-var backgroundPage = ext.backgroundPage.getWindow();
-var require = backgroundPage.require;
+"use strict";
 
-var Services = backgroundPage.Services;
-var Synchronizer = require("synchronizer").Synchronizer;
-var Utils = require("utils").Utils;
-var Prefs = require("prefs").Prefs;
-var FilterStorage = require("filterStorage").FilterStorage;
-var FilterNotifier = require("filterNotifier").FilterNotifier;
+let backgroundPage = ext.backgroundPage.getWindow();
+let require = backgroundPage.require;
 
-var subscriptionClasses = require("subscriptionClasses");
-var Subscription = subscriptionClasses.Subscription;
-var DownloadableSubscription = subscriptionClasses.DownloadableSubscription;
-var filterClasses = require("filterClasses");
-var Filter = filterClasses.Filter;
-var BlockingFilter = filterClasses.BlockingFilter;
-var defaultMatcher = require("matcher").defaultMatcher;
+let Services = backgroundPage.Services;
+let Synchronizer = require("synchronizer").Synchronizer;
+let Utils = require("utils").Utils;
+let Prefs = require("prefs").Prefs;
+let FilterStorage = require("filterStorage").FilterStorage;
+let FilterNotifier = require("filterNotifier").FilterNotifier;
+
+let subscriptionClasses = require("subscriptionClasses");
+let Subscription = subscriptionClasses.Subscription;
+let DownloadableSubscription = subscriptionClasses.DownloadableSubscription;
+let filterClasses = require("filterClasses");
+let Filter = filterClasses.Filter;
+let BlockingFilter = filterClasses.BlockingFilter;
+let defaultMatcher = require("matcher").defaultMatcher;
 
 /**
  * Shortcut for document.getElementById(id)
  */
 function E(id)
 {
   return document.getElementById(id);
 }