I have looked at the bugzilla site, but I was unable to find the problem listed. Seems something like this should have been reported by now. Before I report it, can someone confirm that it's not just my computer?
Open Firefox. Have one open window, and minimize it. Then, try making a New window via the menubar (File->New Window). Mine does nothing. (Command+N does work, however.) In fact, selecting anything in the menu bar right of the "Firefox" menu does nothing.
I'm using the basic Theme, with no others installed. I've checked on another profile, and it does the same thing. The problem has existed for me in the last version also.