For Mozilla 0.9.6 (didn't have this problem in 0.9.5): 1. Start Mozilla (with Quick Launch enabled) 2. Close browser window 3. Attempt to open a window (could be browser, mail, anything) through Quick Launch on Taskbar or a shortcut. Expect: Desired window should open. Get: Nothing happens. "Exit Mozilla" on Quick Launch menu is greyed (as if an instance of the browser is running). I have to use Ctrl-Alt-Del to open the Close Program dialog, kill Mozilla from there, and restart Mozilla.
Sorry, it appears to have been a MultiZilla bug. I tried to uninstall it (MultiZilla), but now that I've wiped Mozilla and done a clean install, I don't have the problem anymore.