In the JFBConnect backend > Configuration > General tab, you will need to configure the 'Auto Username Prefix' option to set it to something more meaningful, like first.last or firlas. Additionally, if you have 'Enable Automatic Registration' set to No and 'Username Field on Registration' option set to "Leave Blank" or "Generate and Show", the user will be able to edit the username value in our login/registration view. If automatic registration is enabled, the username will not be editable.
Changing the above settings should be all that you need to update to fix your issue for both Facebook and Google (or any of the other social networks), so let us know if you continue to run into problems.
-Melissa