https://www.vsynctester.com/ Can confirm the reported issue & catastrphic vsync failure reported when using 69.0a1 (2019-06-14) - Windows 10. Fix verified with 69.0b13 on Windows 10
Bug 1559437 Comment 10 Edit History
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Can confirm the reported issue & catastrphic vsync failure reported on https://www.vsynctester.com/ when using 69.0a1 (2019-06-14) - Windows 10. Fix verified with 69.0b13, 70.0a1 (2019-08-12) on Windows 10, macOS 10.13, Ubuntu 18.04.