https://searchfox.org/mozilla-central/rev/d6188c9ce02efeea309e7177fc14c9eb2f09db37/dom/indexedDB/ActorsParent.cpp#15397,15401 overrides existing mContentParent value, thus causing the release, I think.
Bug 1729422 Comment 5 Edit History
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https://searchfox.org/mozilla-central/rev/d6188c9ce02efeea309e7177fc14c9eb2f09db37/dom/indexedDB/ActorsParent.cpp#15397,15401 overrides existing mContentParent value, thus causing the release, I think. This isn't about holding last reference, but calling release on a wrong thread.