FB had an internal version that predated the FriendFeed one although it wasn’t launched till later. I don’t know what you consider “invented” in the context of silly internet features but that’s the history.

The invention I mean is that when user X likes a post of user Y, the liked post of Y is included into the feeds of users who follow user X. I don't remember this mechanic prior to Friendfeed and then FB. Maybe I'm just unaware of prior art.