Actually it's my proxy server that failed, didn't realise it was an animated GIF and I have it set to deanimate images by default. Ooops!

Odd. It works fine in the stock Android browser.

It actually renders faster than on my desktop. Maybe Firefox has a higher per-frame delay?

That's strange, works fine on Chrome/4.2/Nexus 4. Could you define 'fails'?

Works fine for me with that exact hardware and Chrome.