Please be patient when you post a question. It can take a few hours to get back to a question.
As for your question, there's quite a few ways to do what you're looking for:
* Enable the "Automatically link user's by email" option in JFBConnect. If the Facebook user that just connected has the same email address as a Joomla user in your system, they will automatically be connected
* Use the "Normal Registration" flow. When a user logs in for the first time, they will be brought to a page where they can create a new account or login to an existing one to connect the two.
* In the SCLogin module, enable the "Show Connect Account" option which will show a "Login with Facebook" button to users that are logged in through Joomla but have not associated that account to a Joomla one.
Hope that helps, but if you need anything else, let us know.
Thanks,
Alex