Seen in https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=216630207&repo=try&lineNumber=2731 with test: dom/media/tests/mochitest/test_getUserMedia_GC_MediaStream.html Underlying issue: A task is dispatched to the stable state queue. MediaStreamGraph dispatch all its tasks via nsContentUtils::RunInStableState, including the one from to count DOMMediaStream::CountUnderlyingStreams It seems however that DispatchToMainThreadAfterStreamStateUpdate called from https://searchfox.org/mozilla-central/rev/3160ddc1f0ab55d230c595366662c62950e5c785/dom/media/DOMMediaStream.cpp#354 Will not re-queue the runnable on the main thread as the name indicate, but instead re-add it to the MSG event queue which will then run that task while in stable state. At the very least, if it works as intended, DispatchToMainThreadAfterStreamStateUpdate need to be renamed

Pushed by pehrsons@gmail.com: https://hg.mozilla.org/integration/autoland/rev/83732aea5232 Don't resolve DOMMediaStream::CountUnderlyingStreams promise in stable state. r=jya https://hg.mozilla.org/integration/autoland/rev/feb06b1ef9dd Rename DispatchToMainThreadAfterStreamStateUpdate to DispatchToMainThreadStableState. r=jya,karlt

https://hg.mozilla.org/mozilla-central/rev/83732aea5232 https://hg.mozilla.org/mozilla-central/rev/feb06b1ef9dd