by runawayhorses September 25th 2013, 2:57 am
The facebook login is for members that have already registered to your forum and wish to use their facebook information to login.
If they registered with your forum without using the "fill in the forum with facebook" by clicking the "Associate your facebook account" then they won't be able to login with facebook until they associate their account in their profile page. Those they did fill in the form with facebook would have already associated their accounts during registration and can use the "Login with facebook" anytime they want.
To answer your question, no, guests cannot register automatically right after they click the Sign in with facebook button. They must register the usual way or optionally they can "fill in the forum with facebook' and associate their accounts, then can start to use the "Login with facebook" if they wish. The "facebook Login" is just that, for logging in only.