I tried this both on the FFXI and News styles, and it just leaves the words "Specific Forums" in the box instead of bringing up the list. Also, selecting "Everything" makes the selection box vanish and it won't come back without refreshing the screen.
I'm running Firefox, and while I've got NoScript, it's not blocking Zam or Allakhazam.
It's been a while since I've done a search, so I'm not sure how long this has been a problem.