Change Scroller Icon (like Favicon) How do I change the scroller?

I was reading about browser specific hacks, to hide something from IE, and I found this nice article in the Sitepoint website. As I was reading it, I clicked the middle mouse button (scroller) and instead of the ugly circle with two arrows and a dot in the middle a personalized Icon (of sitepoints logo) appeared. Its kind of like the favicon thing, but with the scroller instead. Anyone here knows how to do this? Or what its called? (scrollicon?, lol, dont know).

It's in the CSS. Looks like it only works for Firefox though. Not sure why it doesn't affect other images on the page though.

html>img /* autoscroll override for Firefox */{	width: 0!important;	height: 28px!important;	padding-left: 28px!important;	background: url(/images/icons/autoscroll2.png);}

but must this code be on the css of a site or in the firefox config files?

but must this code be on the css of a site or in the firefox config files?