Arctic Warrior: have a look at playBunny's remark. it can also be that your firefox browser uses the same setting (regkey) to set gif animation that IE uses. so the setting can be inherited, even if you don't use IE.

you can try also a non-browser program that shows animated gifs, there's a load of free ones on download.com and others. that's just to check if your pb is somehow browser related or something else.