For some reason, the following message is shown in the Javascript console before I even try to authenticate:
Failed to execute 'write' on 'Document': It isn't possible to write into a document from an asynchronously-loaded external script unless it is explicitly opened.
I'm not sure what that means, but it's coming from the following line on your page:
<script type="text/javascript" src="http://www.intensedebate.com/js/genericCommentWrapperV2.js"></script>
I don't know what that is either, but my best suggestion for now is to try and disable that Javascript commenting thing and see if authentication begins to work.
Another option is to go to the Configuration -> Facebook area of JFBConnect and set the "Show credentials in popup" setting to "No". That will do a redirection based login, instead of using the popup authentication window, and may fix your issue.
I hope that helps, but let us know how the above goes.
Thanks,
Alex