The ApplicationAccessible can get shut down by the XPCOM-SHUTDOWN notification while the platform still has references to it and can still call methods on it. That means that if we spin the event loop at all after the accessibility xpcom shutdown observer runs (which can happen) then the platform can currently call methods on a shutdown application accessible. The result of that is assertions that ApplicationAccessible::mAppInfo is null. We can deal with this by having ApplicationAccessible::Shutdown() call AccessibleWrap::Shutdown() so the application accessible gets marked as shutdown. That means that when the platform tries to call methods on it after it has been shut down the generic logic to avoid calling methods on defunct accessibles will kick in and we will bail out before calling methods on the shut down application accessible. One case where the event loop can spin after a11y recieves the xpcom shutdown notification is that the web workers xpcom shutdown observer can run after the a11y one. The web worker observer ends up notifying observers of its own shutdown, and one of the observers of that notification is AsyncShutdown which will spin the event loop during the call to its observer for the web workers shutdown message.

unfortunately I'm not really sure how to write a test that actually covers this issue well other than one that sets up its own observer which seems like more work than its probably worth.

Comment on attachment 8865950 [details] [diff] [review] make ApplicationAccessible::Shutdown() call AccessibleWrap::Shutdown() Review of attachment 8865950 [details] [diff] [review]: ----------------------------------------------------------------- Frightening. I'd sort of prefer comment 1 over this commit message. Can we have a code comment too?

Any advice for next steps on this bug?

(In reply to David Bolter [:davidb] (NeedInfo me for attention) from comment #3) > Any advice for next steps on this bug? I'm sort of confused: the patch is r+ by you. You don't want to take the patch anymore or you want to incorporate some changes into it? What kind of advice do you look for?

I would like to see a test that exhibits the problem we are fixing. Otherwise, I don't really have an opinion on this one way or the other.