Adam,
After logging into your backend, I was able to narrow down the issue to the 'Invitex-User Registration' plugin. When enabled, you cannot log in to your site properly even with Joomla credentials, let alone Facebook via JFBConnect.
To verify that this is not a JFBConnect issue, I disabled our authentication, user and system plugins (which basically renders JFBConnect disabled) and attempted to log in via the Joomla User component at
myfrendz.club/component/users/?view=login and the login username and password at the top (which looks to be just calling the Joomla User component also). I was still not able to log in when the Invitex User Plugin was enabled.
When disabled, everything seems to work fine - logging in via Joomla User Component, logging in via an existing Facebook account with JFBConnect, creating a new account by logging in with Facebook, etc.
I have left the plugin disabled for now. Therefore, if you need this plugin enabled, you will need to make sure the Invitex plugin and component are configured correctly. You will also need to contact the Invitex extension developers for further problems with enabling the plugin.
I hope this helps explain and narrow down the problem for you.
-Melissa