Facebook’s got a special URL for Tor browsers:

Considerations like these have not always been reflected in Facebook’s security infrastructure, which has sometimes led to unnecessary hurdles for people who connect to Facebook using Tor. To make their experience more consistent with our goals of accessibility and security, we have begun an experiment which makes Facebook available directly over Tor network at the following URL:

https://facebookcorewwwi.onion/

[ NOTE: link will only work in Tor-enabled browsers ]

Facebook’s onion address provides a way to access Facebook through Tor without losing the cryptographic protections provided by the Tor cloud.