FYI, I just removed the Facebook login from the forum. It was broken for quite a long time anyhow until very recently and with all the bureaucracy that Facebook now apparently requires around it it quickly became completely unfeasible to uphold.
Login via Twitter, Github, Patreon and Google is still active, as is of course the run of the mill username & password combination.
If you so far only logged in via Facebook, you should be able to request a password reset from the forum using your mail address.