The issue here is on the APZ side: we don't have logic for allowing pull-to-refresh (returning `inputResult` == `INPUT_UNHANDLED`) in the case where the user is panning upward on a scrollable subframe and that subframe is scrolled to the top (such that the scroll is handed off to the root), and the root is also scrolled to the top. This case be seen on a reduced testcase at https://theres-waldo.github.io/mozilla-testcases/div.html: panning upwards over the green area activates pull-to-refresh in Chromium, but not in Firefox.
Bug 1815713 Comment 1 Edit History
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The issue here is on the APZ side: we don't have logic for allowing pull-to-refresh (returning `inputResult` == `INPUT_UNHANDLED`) in the case where the user is panning upward on a scrollable subframe and that subframe is scrolled to the top (such that the scroll is handed off to the root), and the root is also scrolled to the top. This case be seen on a reduced testcase at https://theres-waldo.github.io/mozilla-testcases/div.html: panning upwards over the green area after loading the page activates pull-to-refresh in Chromium, but not in Firefox.