Enabling dither caused a lot of test failures. https://treeherder.mozilla.org/jobs?repo=try&revision=9bc01dba5de5a6f8ec62300de89242a571bf1034
Bug 1968618 Comment 3 Edit History
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Test failure seems not happen by enabling dither only with hardware WebRender. https://treeherder.mozilla.org/jobs?repo=try&revision=410ed038a6c6f9d2a1a529afb71899f48526a60f