After upgrade: "Facebook Javascript library not found"

Rik,
We're still investigating what's happening here, but it doesn't seem to be a JFBConnect-specific issue from what I can see. I'll try to describe everything I've found, and hopefully it will help you narrow things down further.

To function, JFBConnect lets Joomla generate the full page. Then, JFBConnect will alter the code that's in the JResponse output buffer from Joomla. The JResponse code is what Joomla uses to let all the different components, modules and plugins all work together to generate the HTML that is sent to the user.

For some reason, on your home page, and a few select other pages, the JResponse library is behaving differently and not letting any plugins do their alterations to the output HTML before its sent to the user. Specifically, here are some examples:

Output is not behaving properly
/en/
/en/community/forums
/en/community/forums/please-read-before-posting

Output is behaving properly
/en/community

The reason I say the problem isn't specific to JFBConnect is because it seems to be affecting other plugins that do the same modifications that JFBConnect does. On the 'working' page above, there is code for the Google Analytics. That code is missing in the "non working" pages. Just open those pages and search for:

<!-- You can add Google Analytics here-->

In the working page, you'll see the proper Javascript underneath *and* JFBConnect is working properly. In the non-working page, the Analytics is missing and JFBConnect isn't working either.

I don't know what extension is causing this conflict, but it's likely being caused by:
* A module using the wrong code to alter the HTML
* A plugin using the wrong code to alter the output HTML

I tried to disable a variety of system plugins to see if that helped, but I never saw an improvement. You know your site better than I do, and hopefully can help narrow down what plugins/modules may be active on the pages that don't work vs the ones that are enabled on the pages that do work. Then, start disabling those modules/plugins until the Google Analytics code properly shows and the <SCOpenGraphPlaceholder> tags disappears with actual Open Graph tags.

This issue is also (greatly, I'd assume) affecting your Google Analytics results. You may be able to look through those results to see when page hits started dropping off for your home page, and determine what changes (new extensions) you may have made to your site around that time.

I hope that helps explain. I'm not sure why you weren't running into this issue before 6.1. My honest guess is that you were having this problem and just didn't know it, since the JFBConnect functionality properly works on the Community (JomSocial) page, which is where authentication takes place.

Thanks,
Alex

Edited to remove actual links to your site.