2143     // Filter out any nulls for engines that may have been removed
   2144     var filteredEngines = this._sortedEngines.filter(function(a) { return !!a; });
   2145     if (this._sortedEngines != filteredEngines)
   2146       this._needToSetOrderPrefs = true;
   2147     this._sortedEngines = filteredEngines;