Comment 10 for bug 389876

There is a Gnome Human interface guide line:
http://library.gnome.org/devel/hig-book/stable/

What you are actually looking for:
http://library.gnome.org/devel/hig-book/stable/windows-alert.html.en#save-confirmation-alerts

"Save confirmation alerts" - there is a rule for this window. It really makes sense and should be obeyed in all apps. I'd just recommend to put the red cross to "close without saving", because this is actually the most harmfull action.

Well, the pity is: Neither Firefox nor OO.o are gnome-apps.