Make sure the pixel dimensions of the image you upload are at or below the pixel dimensions allowed by the forum.
You can't upload a 150x150 animated gif and expect it to come out OK if the size limit is 80x80. It's probably taking the first frame and dumping the rest when it's
resized, which is what software not specifically designed to deal with animated gifs will do when you try to process something.
You need it to be at or below the maximum size for the forum here _before_ uploading.
You could also try hosting it yourself, then it will just get resized in HTML.