Gifs are an art form?  Do they still require a license? I guess all the relevant patents have now expired.

Yes, the patents have expired. This is big news:

GIF-lovers, rejoice: The web's favorite animation form returned to Facebook on Thursday, thanks to GIF search engine Giphy.

Facebook supported GIFs in "the early days," Giphy co-founder Alex Chung tells Mashable, but stopped supporting them presumably because "they didn't want to look like a MySpace mess with all the blinking garbage on profile pages."

Since then, the GIF has evolved from what Chung describes as "lame clip art" to "an art form." So Giphy worked with Facebook to allow users to share and embed GIFs from giphy.com — at least until Facebook natively supports GIFs again (if it ever does).

Will GIFs overtake Facebook the way they have Tumblr? Probably not to as a great of a degree. The embed format isn't optimal: GIFs don't autoplay, so they function more like short videos.

I just tried to share a gif on Facebook. Didn't work.

This ONLY works for giphy links ?! What is that ???

It's FRUSTRATING, that's what it is!

refinery29 confirms that Facebook gifs only work for Giphy gifs:

http://www.refinery29.com/2013/08/52420/how-to-post-gif-facebook

What?!

Giphy can bite me.