Board Thread:Support Requests - Getting Started/@comment-1824669-20130315144743/@comment-3528606-20130325221539

yes. large gifs that are shrunked wont animate. small gifs that perfectly fit in the thumbnail size will animate. to avoid this, make sure your picture is fully displayed.

to get a smaller gif to play, take it into your animation window (ie ) and resize it

for a more technical explanation: the mediawiki site is not a photo rendering site, and to make all the sizes of the pictures (ranging from tiny: 1px, to very large: 1000px), the mediawiki takes the first picture of the gif and makes it either larger or smaller. the mediawiki framework cannot read the rest of the frames. This is same scenario with the other animation format (but not official): APNGs.