When logging out of Gnome while running non-Gnome applications such as Firefox,
a window appears saying "The following applications do not support saving their
settings and should be saved manually: Mozilla Firefox", or similar words. This
window must be closed manually. If the user logs out of the session and then
leaves the computer before seeing that that window has appeared, then Gnome will
never log out, and this will leave the user logged in. 
The window should display a countdown timer for, say, one minute, and then once
the timer has counted down to zero the window should close as if "Close" was
clicked by the user. Any non-Gnome application which wants the user to save
files or similar is very likely to pop up a "Save open files?" dialog or similar
when Gnome tries to close it anyway.

Other information: