Guess I should try it with the older version of Firefox... may have to switch browsers for posting stuff with multiple photos and/or categories.
Update: Ah, here we go! The Jawascript console reports "Scripts may not close windows that were not opened by script." Sounds like a new security feature. Since the window was opened by... well... actually, the window in question was opened by a script. Of course, it was opened by another script in a different window, but it'd have to be, wouldn't it? Appears to be a Firefox bug.