Michael,
Just got into your site, and was able to really dig into your latest issue. I'm still not sure why the domain isn't showing properly, but hopefully, the below solution will fix you up either way.
When a user tries to register, we load the Joomla User Registration form. This form is generated from the following file:
/components/com_users/models/forms/registration.xml
On your site, that file was completely empty (0 bytes). I'm not sure if this was intentional or not, but that file should have something there. I went ahead and copied the default registration.xml contents, that's distributed with Joomla, and things look great now. I just registered an account without issue, and it seems to be working as expected.
Obviously, test, and let us know if you run into anything else. Also, please let us know if you know why that file may have been blank.. just checking if this is something you did, or something else happened that you didn't know about. It wasn't caused by JFBConnect, either way
Good luck, and thanks for your patience,
Alex