Vreeland,
I'm not sure either. I just tried to Like the same article you posted above, and the popup properly appeared on top. I used Chrome on Windows. If you're using something else, let me know. The popup also properly worked in Chrome.
Looking at the HTML of the page, there's nothing I can see that would cause the popup to go under the other content. The z-index that JFBConnect automatically applies to the social buttons isn't being overwritten and isn't to low of a value (meaning other divs with a z-index are showing up above it).
If you have more information on how your testing, that may help. Also, if you could try from another computer and/or browser to see if you have the same result would help.
Thanks,
Alex