add:  if (!(prefName in this.prefRecords)) return;  
context: function pm_prefchanged(prefName, realValue, oldValue){    for (var i = 0; i < this.observers.length; i++)        this.observers[i].onPrefChanged(prefName, realValue, oldValue);}
meta: 1622	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/1622/f95129b4ef8d32af63069bfe9b732bdcdcd200ca/pref-manager.js/buggy/js/lib/pref-manager.js