Issue 2259 - Removed non-standard JavaScript code from Element Hiding Helper

lib/main.js

Index: lib/main.js
===================================================================
--- a/lib/main.js
+++ b/lib/main.js
@@ -15,13 +15,7 @@
 Prefs.migrate("extensions.adblockplus.ehh.showhelp", "showhelp");
 
 // Window types to attach to
-let knownWindowTypes =
-{
-  "navigator:browser": true,
-  "mail:3pane": true,
-  "mail:messageWindow": true,
-  __proto__: null
-};
+let knownWindowTypes = new Set(["navigator:browser", "mail:3pane", "mail:messageWindow"]);
 
 // Use random marker class
 let elementMarkerClass = null;
@@ -48,7 +42,7 @@
   let styleService = Cc["@mozilla.org/content/style-sheet-service;1"].getService(Ci.nsIStyleSheetService);
   let styleURI = Services.io.newURI("data:text/css," + encodeURIComponent(data), null, null);
   styleService.loadAndRegisterSheet(styleURI, Ci.nsIStyleSheetService.USER_SHEET);
-  onShutdown.add(function() styleService.unregisterSheet(styleURI, Ci.nsIStyleSheetService.USER_SHEET));
+  onShutdown.add(() => styleService.unregisterSheet(styleURI, Ci.nsIStyleSheetService.USER_SHEET));
 }, false);
 request.send(null);
 
@@ -68,7 +62,7 @@
     applyToWindow: function(window)
     {
       let type = window.document.documentElement.getAttribute("windowtype");
-      if (!(type in knownWindowTypes) || window._ehhWrapper)
+      if (!knownWindowTypes.has(type) || window._ehhWrapper)
         return;
 
       window.document.documentElement.appendChild(overlay.cloneNode(true));