MSIE experiences the same problem - it's not a Firefox issue.

There is a 728x90 flash (swf) banner ad in rotation now; it's the very large ad with orange background with black lettering advertising substance-d.com

The work-around is to reload the page until that particular flash ad doesn't appear - then the drop down menu should work ok.

At some point in the future, an alternative search link may be added and/or other changes made to reduce such menu glitches.

Hope this helps.

Ron