The Facebook login support should be deactivated entirely. It was a terrible idea back when it was introduced (and got a lot of criticism) and things like these show that it still is. GOG should take the privacy of their users way more seriously.
I second this. On one side I thank the GOG devs for patching the issue, but on the other side I'd rather see FB's stuff ousted from Galaxy and the website entirely. I believe I do not say falsehood if I state that GOG users are, at least generally speaking, a more conscious bunch when it comes to privacy matters; DRMs ultimately are also about enabling surveillance and from the get-go GOG has been staunchly and rightfully against them.
Social network logins might be a convenience for some people, but maybe the price all users have to pay for that in terms of loss of privacy does not outweigh the "good aspects" of not having to fill in one more registration form and have to memorise one more username/password pair.