Redirecting members not accept the authorization Apllication worm

Florent,
You are including the Facebook Javascript API two times on your site. One time, by JFBConnect. Another time, it looks like it's in a mod_php module. Please disable this 2nd inclusion. You do not want to load the Facebook Javascript Library twice.

Hope this helps.

If you aren't seeing the pop-up. You should add the code above 'jfbc.login.login_custom()'to the following file:
/components/com_user/views/login/tmpl/default_login.php

Florent,
We just did some more testing to force users to log in using Facebook. The below thread may help you:
www.sourcecoast.com/forums/topic?id=2035&p=1#p9200