Everything - videos, GIFs, social media links -- are now part of the MEDIA button (to the right of the Smiley button).
I've noticed that when I just paste a Twitter link right in the reply box, it formats it for me. But apparently for GIFs, you now need to click the Media button, then click the link to the GIF site you want to use, find the GIF there, and then come back here to paste the link. That's more steps than it used to be, unfortunately.