quit_on_closedwindow doesn\'t work on Firefox 1.5

[Nameless]

I am trying to use quit_on_closedwindow parameter.

It works flawlessly on IE 6, but it doesn't work on Firefox.

On Firefox, the user will not exit (until timeout) when s/he closes the window.

[phpfreechat]

I know, this is one of the reason why I didn't activate this parameter by default.
I didn't found a way to detect that the FF browser is going to be closed / reloaded...
If you have ideas about that I will have a look.