--- a/browser/modules/WebappsIconHelpers.js
+++ b/browser/modules/WebappsIconHelpers.js
@@ -11,19 +11,23 @@
  *               aIcons = {
  *                 "16": "http://www.example.org/icon16.png",
  *                 "32": "http://www.example.org/icon32.png"
  *               };
  *
  * @returns the URL string for the largest specified icon
  */
 function getBiggestIconURL(aIcons) {
+  if (!aIcons) {
+    return "chrome://browser/skin/webapps-64.png";
+  }
+
   let iconSizes = Object.keys(aIcons);
   if (iconSizes.length == 0) {
-    return "";
+    return "chrome://browser/skin/webapps-64.png";
   }
   iconSizes.sort(function(a, b) a - b);
   return aIcons[iconSizes.pop()];
 }
 
 /**
  * This function retrieves the icon for an app as specified
  * in the iconURI on the shell object.
@@ -58,17 +62,17 @@ function getIconForApp(aShell, callback)
     if(aShell.useTmpForIcon) {
       let downloadObserver = {
         onDownloadComplete: function(downloader, request, cx, aStatus, file) {
           // pass downloader just to keep reference around
           onIconDownloaded(aShell, mimeType, aStatus, file, callback, downloader);
         }
       };
 
-      tmpIcon = Services.dirsvc.get("TmpD", Ci.nsIFile);
+      let tmpIcon = Services.dirsvc.get("TmpD", Ci.nsIFile);
       tmpIcon.append("tmpicon." + mimeService.getPrimaryExtension(mimeType, ""));
       tmpIcon.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, 0666);
 
       listener = Cc["@mozilla.org/network/downloader;1"]
                    .createInstance(Ci.nsIDownloader);
       listener.init(downloadObserver, tmpIcon);
     } else {
       let pipe = Cc["@mozilla.org/pipe;1"]