Smart favicadvertising

Very often creating new advertising formats simply makes you look desperate. Sheepvertising, spankvertising, selling pixels on your cat etc are all signs of a model in distress.
With some exceptions, of course, like this ad for smart fortwo:

I still wonder how they did it. Favicons are usually .gif or .png files so how can they claim it was "playable"?
Found via talent imitates, genius steals.