When I tested today, video rendering used overlay. Hmm. https://www.youtube.com/watch?v=zCLOJ9j1k2Y
Bug 1849680 Comment 4 Edit History
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When I tested today, video rendering used overlay. Hmm. Build with yesterday m-c caused the problem. Build with today m-c did not cause the problem. change to m-c seemed to addresses the problem. https://www.youtube.com/watch?v=zCLOJ9j1k2Y