Interestingly, I just went to Facebook's developer page to provide you a link for more information on their adaptive width feature. It looks like they've added a new setting that allows you to disable that. We don't have that option in this plugin yet, but you can add it easily. To do so, please edit the /components/com_jfbconnect/libraries/provider/facebook/widget/pageplugin.php file. Around line 33, you'll see:
$tag .= $this->getField('href', 'url', null, '', 'data-href');
Add the following directly underneath that:
$tag .= $this->getField('adapt_width', null, 'boolean', '', 'data-adapt-container-width');
Then, you can update your tag with the new adapt_width setting, like:
{JFBCFacebookPagePlugin width=400 url=<your FB page> adapt_width=false}
You shouldn't need the container div anymore to make that work. The issue with the hidden div is that, even if it has a width of 400px, it's still hidden.. so the width doesn't matter when Facebook is checking. It comes back as 'none'.
Please test and let us know how that goes. We can get this into the next release as well, but would love to have your feedback.
Thanks,
Alex