Olivier,
Thanks for the admin access to your site. You have quite a few components and plugins on your site, which makes narrowing things down more difficult. It also is likely causing your site to load slower than it should. I'd highly recommend going through and disabling or removing any extensions you really aren't using.
With that said, the problem on that page is coming from the following content plugin:
iJoomla Publisher Plugin
I'm not sure what that plugin is doing to prevent JFBConnect from altering the output of the page, but with it disabled, things work fine. JFBConnect is also working fine on all non-content pages, which means that it's something specific to that plugin.
I'd recommend contacting the iJoomla developers to see if they can help investigating what their plugin may be doing and hopefully they'll be able to help you narrow things down.
Of course, keep me posted on what you find and if you need anything else.
Thanks,
Alex