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: 1567	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/1567/fde2b7fccb5e4e87266145d9253d79bb5a9e5fb8/pref-manager.js/clean/js/lib/pref-manager.js