If you want to use imgbb.com to upload your animated GIF, you can just use the "Add image to post via . . . ." button. You can skip the step to copy/paste the Direct Link. It works just fine. The only thing is that you need to add a note saying . . ."Click on image for larger size".
Here is an example of updating an animated GIF via imgbb (not using Direct Link). This was quite a large file -- 1774 x 410 px, 1.3 MB.