Yes, it works fine for me on test sites.
The way it should work is as follows:
1. You attempt to go to any page which needs authentication, like /wp-admin. The wp-login.php loads instead (this is normal WordPress).
2. You click the FB login button. If you're not logged into FB, you get the popup. If you are, then the popup appears but probably immediately disappears.
3. After logging into FB, the wp-login.php page reloads. At this point, SFC kicks in on the back end and recognizes that you have FB credentials in your cookies.
4. The cookies are parsed and your Facebook ID is determined. If your ID is already connected to an existing WP account, then you're logged in as that account. Else, your email from Facebook is checked and a WP user is found with the same email, and you are then logged in as that user. Either way, you're directed to wherever you were headed before (like /wp-admin for example), because you're now logged in as far as WP cares.
5. If you have no ID or email match, the login page loads and displays the message: "Cannot log you in. There is no account on this site connected to that Facebook user identity."