What do you mean at a clearnet site? Signing up through open wifi or something? You could do that, but Facebook gives a lot of shit to accounts that change IP addresses all the time. It triggers their spammer algorithms and your account may end up on various levels of lock down, unable to send messages to others, comment on their status updates, etc., they may require you to phone verify (which you could do with a burner), or they could shut down your account without warning.