Problem exists only on FireFox (from 3.6 up to current 9), other browsers are fine. My code looks like this:
jQuery.extend({
AnchorFromUrl : function(url) {
I noticed this behaviour, too. Every now and then Firefox drops a favicon or it refuses to put the favicon alongside my bookmark. I think this is a Firefox bug.
To workaround this (and for other functionality), I installed the Favicon Picker add-on. Of course, this doesn't solve your problem on other computers, like clients and the like.