use throbber to indicate busy on List source, so much better than a static image.

content/collections.css

@@ -92,13 +92,13 @@
 
 /* Collection loading/refreshing indicator */
 #sourcesViewTreeChildren::-moz-tree-image(isBusy) {
-/* XXX: argh, an animated image in the tree will cause a low level race condition
+/* XXX: Try the animated image.  Possibly causes a low level race condition
  * which increases with number of rows with the image, after the image is no longer
  * valid for a row property; no amount of view nulling etc etc could fix this.
  * It seems the tree keeps invalidating itself once an anim image is loaded.
-  list-style-image: url("chrome://global/skin/icons/loading_16.png");
-*/
   list-style-image: url("chrome://snowl/content/icons/arrow_refresh_small.png");
+*/
+  list-style-image: url("chrome://global/skin/icons/loading_16.png");
 }
 
 /* Error on collection indicator */

content/collections.js

@@ -1569,7 +1569,7 @@ function SnowlTreeViewGetImageSrc(aRow, aColumn) {
     nodeStats = {t:0, u:0, n:0};
 
   if (!this._visibleElements[aRow].icon ||
-      (nodeStats && (nodeStats.n || nodeStats.busy)) ||
+      (nodeStats && nodeStats.n) ||
       (source && (source.busy || source.error ||
       (source.attributes.refresh &&
       (source.attributes.refresh["status"] == "disabled" ||