1672495 - Don't flash nested-subframe scrollbars on inital page reflow

Status: NEW

(Core :: Panning and Zooming, defect, P3)

Description

[[ex-Mozilla] Agi Sferro | :agi]

Gecko flashes scrollbars on Android on page load which is a little bit jarring. It would be nice if we didn't.

Comparison with Chrome: https://imgur.com/a/qJUGfS9

Comment 1

[Timothy Nikkel (:tnikkel)]

To be specific, there are scrollbars shown under 'ALL NEWS BOOKS' and under the day selector for the weather. There is also one shown for the root scroll frame.

Comment 2

[Kartikaya Gupta (email:[e-mail])]

(In reply to Agi Sferro | :agi | ⏰ PST | he/him from comment #0)

Comparison with Chrome: https://imgur.com/a/qJUGfS9

The Chrome video also has scrollbars flashing, just for a very brief time.

Comment 3

[Kartikaya Gupta (email:[e-mail])]

My mistake, I was looking at the root scrollbar. This bug is about the subframe scrollbars.

Comment 4

[Markus Stange [:mstange]]

The scrollbar is probably shown because we hit one of the ActivityOccurred() calls in nsGfxScrollFrame.cpp.
As a potential fix, we could skip the call for non-mIsRoot scroll frames when it is encountered for the first time. But this behavior should be controlled by a new LookAndFeel flag. We want to keep flashing subframe scrollbars on macOS.