Comment 81 for bug 73536

(sorry, by which I meant to say more specifically: 'killall firefox' has the same issue, it prompts a session crash dialog for me on next startup. It's just not something I use often since I usually use the close button which works, but on shutdown the same mechanism is used - of course with a timeout as you correctly state, but that doesn't help when it doesn't even work correctly with no timeout)