Admin drop down menus in Firefox: not working

Using Zen Cart 1.3.8a, and Firefox 3.5.4 (latest v.) on a macbook pro 2.53 running Snow Leopard (OS X 10.6)
PROBLEM: I don't see this posted anywhere else. Since I installed the newest version of Firefox, the drop down menus will not drop down in Admin. I can only click on the top menu item in each of the menus. As soon as I mouse down over what the menu contains below the top item - the menu disappears again.

This is really a drag. Can someone look into this, I've given the versions above, so the problem can be re created.

thanks, JSC, Boulder :censored:

FYI, it works OK in that FF version on XP, so you either got a corrupted installation, or there's a bug in the Mac version.