add:  var obs = Components.classes["@mozilla.org/observer-service;1"]. getService(Components.interfaces.nsIObserverService); obs.removeObserver(clearDownloadsObserver, "download-manager-clear-history"); 
context: function Shutdown() {  gDownloadManager.removeListener(gDownloadListener);}
meta: 10520	/local1/tlutelli/issta_data/temp/all_js/javascript/2007_temp/2007/10520/1a8487d77605aba2290b29c5c9e553ec93d2f90d/downloads.js/buggy/toolkit/mozapps/downloads/content/downloads.js