I noticed recently that we have this code in RuntimeService::CancelWorkerForWindow(): if (worker->IsSharedWorker()) { worker->CloseSharedWorkersForWindow(aWindow); } else if (!worker->Cancel(cx)) { JS_ReportPendingException(cx); } But then in WorkerPrivateParent::CloseSharedWorkersForWindow() we have: MOZ_ASSERT(IsSharedWorker() || IsServiceWorker()); It seems to me that either the first one needs: if (worker->IsSharedWorker() || worker->IsServiceWorker()) { worker->CloseSharedWorkersForWindow(aWindow); } Or we need to restrict MOZ_ASSERT in the second case.

Seems like this could be the source of some crashers in our SW tests as the worker might not get shutdown properly when the document goes away.

Added the IsServiceWorker() check to RuntimeService. This will at least decrease the 'reference count' of the WorkerPrivate in a sane way when client JS is holding on to ServiceWorker instances when the window goes away. I'm not sure if that prevents any crashes though.