With Attachment 9470695 [details] [diff], when the problem happened, [PresShell::ComputeActiveness()](https://searchfox.org/mozilla-central/rev/35ee3edf7841310b798a14a4fe6f82e21e357df3/layout/base/PresShell.cpp#11522) returned true because "browserChild->IsPreservingLayers()" returned false. Then nsRefreshDriver was set active and keeps ticking.
Bug 1952787 Comment 2 Edit History
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With Attachment 9470695 [details] [diff], when the problem happened, [PresShell::ComputeActiveness()](https://searchfox.org/mozilla-central/rev/35ee3edf7841310b798a14a4fe6f82e21e357df3/layout/base/PresShell.cpp#11522) returned true because "browserChild->IsPreservingLayers()" returned false. Then nsRefreshDriver was set active and kept ticking.
With Attachment 9470695 [details] [diff], when the problem happened, [PresShell::ComputeActiveness()](https://searchfox.org/mozilla-central/rev/35ee3edf7841310b798a14a4fe6f82e21e357df3/layout/base/PresShell.cpp#11522) returned true because "browserChild->IsPreservingLayers()" returned false. Then nsRefreshDriver was set active and it kept ticking.