So looking at the reftest on desktop, it looks like the testcase's `<input type="range">` slider-widgets are legitimately skinnier than the reference case's widgets. However, their background is transparent (and the container is wide enough that it doesn't matter for sizing/positioning purposes), so you can't tell. With that information and the reftest-analyzer visualization, it seems that the problem here is that we somehow started triggering a non-transparent background for these sliders on Android. That's semi-believable since this patch did touch `widget/android/nsLookAndFeel.cpp`, but in a way that wouldn't be expected to have any effect...
Bug 1592389 Comment 11 Edit History
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So looking at the reftest on desktop, it looks like the testcase's `<input type="range">` slider-widgets are legitimately skinnier than the reference case's widgets. However, their background is transparent (and the container is wide enough that it doesn't matter for sizing/positioning purposes), so you can't tell. With that information and the reftest-analyzer visualization, it seems that the problem here is that we somehow started triggering a non-transparent default background for these sliders on Android (which then reveals the otherwise-hidden fact that their widths are different between the testcase and reference case). That is semi-believable since this patch did touch `widget/android/nsLookAndFeel.cpp`, but in a way that wouldn't be expected to have any effect...