Facebook and Tor
A number of users have noticed that Facebook is blocking connections from the Tor network. Facebook is not blocking Tor deliberately. However, a high volume of malicious activity across Tor exit nodes triggered Facebook's site integrity systems which are designed to protect people who use the service. Tor and Facebook are working together to find a resolution.
For further questions please contact us at email@example.com.
Update from Facebook on June 18, 2013, 2:30 PM EST: Facebook's site integrity systems detected automated malicious activity coming from a significant number of Tor exit nodes. In order to protect people while we investigated the problem, access via these nodes was temporarily suspended. This issue has now been resolved and Tor access routes to Facebook restored.
Works fine for me - just logged on to facebook from Tor. Probably just one exit router.