People connect to Facebook in many different ways, which is why we have implemented HTTPS across our service, and Perfect Forward Secrecy, HSTS, and other technologies which help give people more confidence that they are connected securely to Facebook.
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, they have begun an experiment which makes Facebook available directly over Tor network at the following below URL this link will only work in Tor-enabled browsers:
https://facebookcorewwwi.onion/
The idea is that the Facebook onion address connects you to Facebook's Core WWW Infrastructure - check the URL again, you'll see what we did there and it reflects one benefit of accessing Facebook this way: that it provides end-to-end communication, from your browser directly into a Facebook datacentre.
they are decided to use SSL atop this service due in part to architectural considerations - for example, we use the Tor daemon as a reverse proxy into a load balancer and Facebook traffic requires the protection of SSL over that link.
