It happens when firefox window is not focused when launched. I can do this under GNOME for example having a terminal window with the "always on top" activated and launching firefox from a panel launcher or Alt+F2 dialog. In that case firefox opens, requests the focus to the window manager (metacity won't give it because of the focus stealing prevention) and no document:load-complete is fired.
Doing the same with firefox 3.6 and it fires the document:load-complete
I finally found a way to reproduce it.
It happens when firefox window is not focused when launched. I can do this under GNOME for example having a terminal window with the "always on top" activated and launching firefox from a panel launcher or Alt+F2 dialog. In that case firefox opens, requests the focus to the window manager (metacity won't give it because of the focus stealing prevention) and no document: load-complete is fired.
Doing the same with firefox 3.6 and it fires the document: load-complete