I've been thinking about how to investigate this. I think a starting point might be to reproduce the issue with [apz.retarget](https://searchfox.org/mozilla-central/rev/e69f323af80c357d287fb6314745e75c62eab92a/layout/base/PositionedEventTargeting.cpp#43) logging enabled. This will log the touch events that arrive at the content process when you tap, including their: 1. coordinates 2. initial event target (based on their coordinates) 3. final (re-targeted) event target (The frame tree, dumped [here](https://searchfox.org/mozilla-central/rev/e69f323af80c357d287fb6314745e75c62eab92a/layout/base/PositionedEventTargeting.cpp#589-595) only at the verbose logging level (level 5), is particularly helpful to understand where in the document the elements targeted at steps 2 and 3 are.) We can then correlate this information with the document structure viewed in the Inspector using `about:debugging` to understand at which point the observed results start to diverge from expectations.
Bug 1889017 Comment 10 Edit History
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I've been thinking about how to investigate this. I think a starting point might be to reproduce the issue with [apz.retarget](https://searchfox.org/mozilla-central/rev/e69f323af80c357d287fb6314745e75c62eab92a/layout/base/PositionedEventTargeting.cpp#43) logging enabled. This will log the touch events that arrive at the content process when you tap, including their: 1. coordinates 2. initial event target (based on their coordinates) 3. final (re-targeted) event target (The frame tree, dumped [here](https://searchfox.org/mozilla-central/rev/e69f323af80c357d287fb6314745e75c62eab92a/layout/base/PositionedEventTargeting.cpp#589-595) only at the verbose logging level (level 5), is particularly helpful to understand where in the document the elements targeted at steps 2 and 3 are.) We can then correlate this information with the document structure viewed in the Inspector using [about:debugging](https://firefox-source-docs.mozilla.org/devtools-user/about_colon_debugging/index.html) to understand at which point the observed results start to diverge from expectations.
I've been thinking about how to investigate this. I think a starting point might be to reproduce the issue with [event.retarget](https://searchfox.org/mozilla-central/rev/e69f323af80c357d287fb6314745e75c62eab92a/layout/base/PositionedEventTargeting.cpp#43) logging enabled. This will log the touch events that arrive at the content process when you tap, including their: 1. coordinates 2. initial event target (based on their coordinates) 3. final (re-targeted) event target (The frame tree, dumped [here](https://searchfox.org/mozilla-central/rev/e69f323af80c357d287fb6314745e75c62eab92a/layout/base/PositionedEventTargeting.cpp#589-595) only at the verbose logging level (level 5), is particularly helpful to understand where in the document the elements targeted at steps 2 and 3 are.) We can then correlate this information with the document structure viewed in the Inspector using [about:debugging](https://firefox-source-docs.mozilla.org/devtools-user/about_colon_debugging/index.html) to understand at which point the observed results start to diverge from expectations.