Hey! Here's a quick and easy to follow step by step on how to comment gifs:
Step one: Generate or copy the link to the gif you want to use! (It will look something like this: https://imgflip.com/(gif)/(image/gif code))
Step Two: When you go to comment hit the add image button.
Step Three: Paste the link into the the pop up and click "insert image" then post your comment! Boom done! Hope this helps! 👍