Issue 340 - Element hiding reports NS_ERROR_NOT_AVAILABLE to error console

lib/elemHide.js

 /*
  * This file is part of Adblock Plus <http://adblockplus.org/>,
  * Copyright (C) 2006-2014 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 235 matching lines @@
 
       TimeLine.leave("ElemHide.apply() done (no file changes)");
       return;
     }
 
     IO.writeToFile(styleURL.file, this._generateCSSContent(), function(e)
     {
       TimeLine.enter("ElemHide.apply() write callback");
       this._applying = false;
 
-      if (e && e.result == Cr.NS_ERROR_NOT_AVAILABLE)
-        IO.removeFile(styleURL.file, function(e2) {});
+      // _generateCSSContent is throwing NS_ERROR_NOT_AVAILABLE to indicate that
+      // there are no filters. If that exception is passed through XPCOM we will
+      // see a proper exception here, otherwise a number.
+      let noFilters = (e == Cr.NS_ERROR_NOT_AVAILABLE || (e && e.result == Cr.NS_ERROR_NOT_AVAILABLE));
+      if (noFilters)
+      {
+        e = null;
+        IO.removeFile(styleURL.file, function(e) {});
+      }
       else if (e)
         Cu.reportError(e);
 
       if (this._needsApply)
       {
         this._needsApply = false;
         this.apply();
       }
-      else if (!e || e.result == Cr.NS_ERROR_NOT_AVAILABLE)
+      else if (!e)
       {
         ElemHide.isDirty = false;
 
         ElemHide.unapply();
         TimeLine.log("ElemHide.unapply() finished");
 
-        if (!e)
+        if (!noFilters)
         {
           try
           {
             Utils.styleService.loadAndRegisterSheet(styleURL, Ci.nsIStyleSheetService.USER_SHEET);
             ElemHide.applied = true;
           }
           catch (e)
           {
             Cu.reportError(e);
           }
@@ skipping 110 matching lines @@
       let filter = filterByKey[key];
       if (specificOnly && (!filter.domains || filter.domains[""]))
         continue;
 
       if (filter.isActiveOnDomain(domain) && !this.getException(filter, domain))
         result.push(filter.selector);
     }
     return result;
   }
 };