add: document.getElementById("editFeed").disabled = !item || item.container; 
context:   onSelect: function ()   {    var properties, item;    var seln = this.mTree.view.selection;    item = this.mView.getItemAtIndex(seln.currentIndex);          this.updateFeedData(item);            document.getElementById("removeFeed").disabled = !item || item.container;  },
meta: 5459	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/5459/ed68096f45d67e0b0f89efbd51c1a68f99ff07ba/feed-subscriptions.js/clean/mail/extensions/newsblog/content/feed-subscriptions.js