I guess I don't see the point of using Tor with Facebook. So much of your identity is already tracked. It's like trying to sneak up on somebody while wearing those squeaky clown shoes.
When you have a very small subset of users who will go through the trouble of trying out Facebook's onion address, it is much easier to be successful with surveillance tools on that small sample.
Because not everyone uses their real name on Facebook, especially in a Middle Eastern country, I would imagine. And Facebook isn't just for your family and real friends anymore (and hasn't been for years).