[We fire WidgetTouchEvent for pens](https://searchfox.org/mozilla-central/rev/f60bb10a5fe6936f9e9f9e8a90d52c18a0ffd818/widget/nsBaseWidget.cpp#1215-1237) to achieve Windows scroll-by-pen behavior, which is managed by the pref `dom.w3c_pointer_events.scroll_by_pen.enabled`. My current assumption is that APZ assumes all WidgetTouchEvent is from touch input and [applies TouchBlockState](https://searchfox.org/mozilla-central/rev/f60bb10a5fe6936f9e9f9e8a90d52c18a0ffd818/gfx/layers/apz/src/InputQueue.cpp#110). Maybe we should disable this by checking mInputSource.
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[We fire WidgetTouchEvent for pens](https://searchfox.org/mozilla-central/rev/f60bb10a5fe6936f9e9f9e8a90d52c18a0ffd818/widget/nsBaseWidget.cpp#1215-1237) to achieve Windows scroll-by-pen behavior, which is managed by the pref `dom.w3c_pointer_events.scroll_by_pen.enabled`. My current assumption is that APZ assumes all WidgetTouchEvent is from touch input and [applies TouchBlockState](https://searchfox.org/mozilla-central/rev/f60bb10a5fe6936f9e9f9e8a90d52c18a0ffd818/gfx/layers/apz/src/InputQueue.cpp#110). Maybe we should disable this by checking mInputSource (or add WidgetPenEvent? 🤔)