Today, both of Facebook's current apps have been updated to prepare for the arrival of Facebook Home. The main app merely added an extra permission that Home will eventually use. However, the real fun came to Messenger, which now has the ability to pop out Chat Heads, regardless of if you're using the replacement launcher.
As you may recall from the Facebook Home launch event, chat heads are little bubbles that float over whatever you're doing and allow you to jump straight into a conversation no matter where you are in the OS. Just tap your friend's face and an IM window appears.