Elisabeth,
If you look at the HTML code from your page using the View Source option in Firefox, or any other extension, you can see that the Facebook Javascript library is being loaded twice. Search for "all.js" and you'll see 2 blocks of code one above the other. The first block is from JFBConnect. The 2nd block is from something else. You'll need to remove that extra block as it's causing your issue.
I don't know what's inserting that, or I'd help more. It could be included by a plugin, component, or something in your template directly.
Hope that helps get you started, and good luck,
Alex