GIFs are slowly starting to creep into the Facebook News Feed. While GIFs have been supported (though not in auto-play fashion) for personal posts since May, the company is testing the feature on page posts.
A Facebook spokesperson confirmed this to Facebook:
GIFs can be a fun and compelling way to communicate, so we’ve started testing GIF support in posts and boosted posts for a small percentage of Facebook Pages. We will evaluate whether it drives a great experience for people before rolling it out to more Pages.
You can find some examples of existing GIF posts here: