Damiaan,
First, I'd recommend trying to add the following style to your template, which will hopefully fix it:
.scsocialbuttons {z-index: 110 !important }If you're not sure where to put it in, just place it at the bottom of /templates/joomla29november/css/template.css
I believe that should fix you right up, but if not, the following code change definitely will (but it can be overwritten if you upgrade JFBConnect, so the method above is better). In the /plugins/content/jfbccontent.php file, at line 245, you'll see:
$buttonText = '<div style="position: relative; top:0px; left:0px; z-index: 100;" class="scsocialbuttons">';
In that block, update the z-index value to be 110.
Hope that helps!
Alex