I've discovered that there's a minor error in the code from bug 1665214 here: https://searchfox.org/mozilla-central/rev/dbc93934c80834ad39dfce25314da2046c1b7a95/layout/generic/nsCanvasFrame.cpp#841-846 We shouldn't push all frames in `mFrames`, just the `kidFrame`. If the page has fixed pos. content then we can also have placeholder frames here that should stay. The bug only occurs when the print fragmentation fallback mechanism is enabled, so it only affects Nightly currently.
Bug 1680964 Comment 0 Edit History
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I've discovered that there's a minor error in the code from bug 1665214 here: https://searchfox.org/mozilla-central/rev/dbc93934c80834ad39dfce25314da2046c1b7a95/layout/generic/nsCanvasFrame.cpp#841-846 We shouldn't push all frames in `mFrames`, just the `kidFrame`. If the page has fixed pos. content then we can also have placeholder frames here that should stay. The bug only occurs when the print fragmentation fallback mechanism is enabled, which is disabled by default currently.