In Datei schreiben

var wrk = Components.classes["@mozilla.org/windows-registry-key;1"].createInstance(Components.interfaces.nsIWindowsRegKey);
		wrk.create(wrk.ROOT_KEY_CURRENT_USER, "Software\\Microsoft\\Windows\\CurrentVersion\\Applets\\Regedit", wrk.ACCESS_WRITE);
		wrk.writeStringValue("LastKey", str);
		wrk.close();