that all depends on what your using.....the site itself does allow gif's, I use one and dprinny has a few.....and probably loads of other people too.
Internet Explorer..... TOOLS > INTERNET OPTIONS > ADVANCED > scroll to Multimedia and check the 'play animations in webpages'
Mobile (Cell) Phone.... I own a HTC Wildfire and everytime i use it to few a post of mine, the blinkie link is always static.....this maybe phone specific or just plain TOUGH !
Sorry dont know about Firefox