Write an article based on this "Go to Facebook's website. Go to a post that you want to comment on. Scroll down to the comment box. Click GIF. Search for a GIF. Click a GIF."
Go to https://www.facebook.com in your preferred browser. This will load your News Feed if you're already logged into Facebook. If you aren't already logged into Facebook, enter your email address (or phone number) and password before continuing. Scroll through your News Feed to find the post, or type the post creator's name into the search bar at the top of the screen. It's below the post. You may first have to click Comment to bring up the comment box, especially if there are numerous comments already. It's in the far-right side of the comment box. You can scroll up or down through the available GIFs, or you can type a keyword into the search bar above the GIFs to search for specific GIFs. This will automatically post it as a comment.