There are some animated gif's of Firefox eating Explorer and such like here....Not sure if you could use any of them as an Avatar or not though....
http://homeusers.brutele.be/jpbardia...if/anigif.html
The main site also has banners, buttons and more...Some of them are quite good, some not so...
http://homeusers.brutele.be/jpbardiau/
Regards
David