When you open the Facebook page, you can comment on a friend's post with GIF which is a short moving image. The reaction option with the GIF is an icon labeled "GIF" next to emoji icons, stickers, and attach photos, as well as videos.
GIF on Facebook's core social networking is basically similar to GIF on the Facebook Messenger chat service. There are some colleagues who are embraced as GIF providers, namely Giphy, Tenor, and Disney.
Note that you can only use GIF from the search provided in the comments field. That is, GIF is just from partner Facebook.
You can not upload your own GIF to react to friends' posts, as Mashable reported and compiled KompasTekno, Friday (16/06/2017).
