It seems that, since a few weeks, Firefox no longer closes a window when pressing ctrl-w even if there is only one tab in the window. What I mean is that, if I open a new window (ctrl-n), it won't close if I press ctrl-w (or ctrl-F4) immediately after. If there's is one window with one tab, the application won't close. ctrl-shift-w won't close all windows as it used to either. I've tried finding a preference about this that could have been deactivated by mistake, but couldn't find anything.