See bug 1260461 for greater context, but the TL;DR is that when a user has Firefox open, and they log out of / shut down Windows without quitting the browser, then Firefox receives a message that causes it to try to quit. We added stuff in bug 1177310 to block the quit-application-granted observer notification while we wait for the async messages to come up from each browser with session updates. Unfortunately, in bug 1260461, we noticed that Windows was killing our process before we could complete shutdown properly. We created a band-aid fix in bug 1260461 which causes us to write the cached snapshot of our most recent session updates to disk and do an immediate shutdown. This has the (small but very real) potential for dataloss, since the session might have changed since the last snapshot. We should try to figure out why Windows is killing our process before we can shut down properly, and fix it.
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