Facebook is no longer blocking visitors using the Tor anonymity service to access the social network. Facebook s automated malware detection system temporarily blocked visitors who use the Tor service. The issue has since been resolved and Tor users are again able to access Facebook. Tor is a free tool that keeps Web browsing sessions private and anonymous. It has become a vital instrument for activists living in oppressed parts of the world to communicate with followers they otherwise would not be able to reach. The tool is a favorite, not only for privacy conscious users, but people concerned about censorship.
Source: https://threatpost.com/facebook-restores-connections-to-tor-users-after-malware-spike/101036/