Where does it not move? In your composition window? Or in test messages sent to yourself and viewed in Thunderbird? I wouldn't expect animation in the Compose window. It's a slightly odd environment where links don't work, frames are shown as dotted lines etc. Whether or not an animated gif shows as animated depends on the program being used to view it. I'd expect Firefox to be able to do this and so, by extension, I'd be surprised if Thunderbird can't, since both use the same rendering engine. But I don't have Thunderbird here with me right now to check. However ISTR having seen moving images in Thunderbird. As you may have guessed from my uncertainty about this, I don't often get messages containing animations.