firefox message is it an error or not

[Alan Cox]

> Apparently, there is no equivalent in X-Windows. When an X server 

Not the case

> terminates, it just tears down all client connections, apparently. From an 
> application's point of view there may not actually be a way to detect if the 
> X connection went away because of a server crash, or the user logging off.

At the lowest level X itself doesn't care about this. The toolkits and
window managers do and there is a session management system implemented
by the toolkit/desktop (eg by gnome-session). Programs are told politely
to quit first (eg if you hit the window destroy button). Gnome then uses
a dialog and asks the user if it can kill the window if nothing occurs
within a timeout.