disable update button on nonupdateable feeds

js/viewfeed.js

@@ -53,6 +53,10 @@ function headlines_callback2(transport, offset, background, infscroll_req) {
 
 			setActiveFeedId(feed_id, is_cat);
 
+			dijit.getEnclosingWidget(
+				document.forms["main_toolbar_form"].update).attr('disabled',
+					is_cat || feed_id <= 0);
+
 			try {
 				if (offset == 0 && infscroll_req == false) {
 					$("headlines-frame").scrollTop = 0;