I hate to break this to you but they’ve had it for decades. fb.com rewrites to facebook.com

I think you’d loose ownership over the domain because you own it explicitly to take it hostage before facebook.
And because they have a trademark I think they could seize it.
Probably except if you have something like the matching initials or other reasons for why you’d have a right to it.

But I don’t know if that is true.