--- a/mailnews/extensions/newsblog/content/Feed.js
+++ b/mailnews/extensions/newsblog/content/Feed.js
@@ -42,31 +42,36 @@ const kNewsBlogInvalidFeed = 1; // usual
 const kNewsBlogRequestFailure = 2; // generic networking failure when trying to download the feed.
 const kNewsBlogFeedIsBusy = 3;
 const kNewsBlogNoNewItems = 4; // there are no new articles for this feed
 
 // Cache for all of the feeds currently being downloaded, indexed by URL, so the load event listener
 // can access the Feed objects after it finishes downloading the feed.
 var FeedCache = 
 {
-  mFeeds: new Array(),
+  mFeeds: {},
 
   putFeed: function (aFeed)
   {
     this.mFeeds[this.normalizeHost(aFeed.url)] = aFeed;
   },
 
   getFeed: function (aUrl)
   {
-    return this.mFeeds[this.normalizeHost(aUrl)];
+    var index = this.normalizeHost(aUrl);
+    if (index in this.mFeeds)
+      return this.mFeeds[index];
+    return null;
   },
 
   removeFeed: function (aUrl)
   {
-    delete this.mFeeds[this.normalizeHost(aUrl)];
+    var index = this.normalizeHost(aUrl);
+    if (index in this.mFeeds)
+      delete this.mFeeds[index];
   },
 
   normalizeHost: function (aUrl)
   {
     var ioService = Components.classes["@mozilla.org/network/io-service;1"].
                     getService(Components.interfaces.nsIIOService);
     var normalizedUrl = ioService.newURI(aUrl, null, null);
     normalizedUrl.host = normalizedUrl.host.toLowerCase();