Comment 60 for bug 73536

This is a problem for geckodriver and for anything else that's using marionette to control the browser (e.g. various test harnesses including wpt). If we don't shut down the browser gracefully we lose out on the ability to do various things that depend on clean shutdown (certainly leak logging, perhaps code coverage). Marionette has a method to invoke shutdown, but sending the response races with closing the marionette connection, so it isn't reliable. Signalling the process with SIGTERM would be the obvious solution, except for this bug. So we either need a way to ensure that the marionette response is sent before the corresponding socket is closed, or a fix here.