1747024 - Not able to scroll page "ps-blog-game-of-the-year-2021-the-winners" (Lady Dimitrescu keeps reappearing in scrollport)

Status: RESOLVED WORKSFORME

(Core :: Layout: Flexbox, defect)

Description

[Patrick (he/him)]

Steps to reproduce:

1. Navigate to https://blog.playstation.com/2021/12/20/ps-blog-game-of-the-year-2021-the-winners/

2. Scroll down page using scrollbar

Expected result: Able to scroll page
Actual result: Page gets stuck in a loop and won't scroll past a certain section

Regression - last good build 2020-11-03, first bad build 2020-11-04 - unable to bisect further

Comment 1

[Gian-Carlo Pascutto [:gcp]]

Working on Nightly on macOS.

Comment 2

[Jens Stutte [:jstutte]]

On Windows Nightly I can see the issue here. Scrolling down shows several times the same content and after scrolling down a while, scrolling up will show a blank canvas. Let's start the investigation from DOM: Events.

Comment 3

[Jens Stutte [:jstutte]]

This is not a recent regression. To me it happens also with Fx90.

Comment 4

[Ryan VanderMeulen [:RyanVM]]

Possible regression range based on comment 0:
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=8e58925909cccd52a321809d5094d96e7979ed0e&tochange=2977d4891ceeed019dc906dff3feb6c9f530213c

At first glance, this stands out:

Bug 1671526, use DispatchInputEvent for drag events on windows, r=kats
https://hg.mozilla.org/mozilla-central/rev/b6d258866337047ef3aa51f629e026c9d5dd5cf4

Comment 5

[Neil Deakin]

Unlikely. That code will only get called during a drag/drop operation.

This looks more like a rendering issue, and I see similar glitchiness on Mac as well.

Comment 6

[Edgar Chen [:edgar]]

(In reply to Jens Stutte [:jstutte] from comment #2)

On Windows Nightly I can see the issue here. Scrolling down shows several times the same content and after scrolling down a while, scrolling up will show a blank canvas. Let's start the investigation from DOM: Events.

I could also reproduce the same glitchiness on Mac and I got following regression range,

4:13.91 INFO: Last good revision: fb2b08c6bc8c320127586fcedb2626e496bf3dcf (2020-07-07)
4:13.91 INFO: First bad revision: ee89deeb4fb6d12456c551c5ab4aaae151ceedae (2020-07-08)
4:13.91 INFO: Pushlog:
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=fb2b08c6bc8c320127586fcedb2626e496bf3dcf&tochange=ee89deeb4fb6d12456c551c5ab4aaae151ceedae

Comment 7

[Alice0775 White]

Scrolling down shows several times the same content

I can reproduce the issue on Windows10.

Regression window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=3a38af2b7e83456941bed532016ae31208589dd0&tochange=1aa53285261e17aa6a8b36e05c7208d616c24aa4

Comment 8

[Jens Stutte [:jstutte]]

Bug 1492538 appears in both regression ranges. Daniel, could you take a look and in case confirm the regression?

Comment 9

[Daniel Holbert [:dholbert]]

Attachment: diagnostic patch (adds a pref that can be enabled to turn off a flexbox optimization)

(In reply to Jens Stutte [:jstutte] from comment #8)

Bug 1492538 appears in both regression ranges. Daniel, could you take a look and in case confirm the regression?

I confirmed it is a regression from that change, yeah.

Here's a diagnostic patch that lets you disable the optimization that we added in that bug. With this patch applied (and with the included pref layout.css.flex.perf.cache-final-reflow.disabled manually set to true), the bug does not reproduce.

My STR for testing this are as follows (simpler/more-reliable than using the scrollbar IMO):
(1) Load https://blog.playstation.com/2021/12/20/ps-blog-game-of-the-year-2021-the-winners/
(2) Press pagedown 3-4 times, until you see the picture of a Lady Dimitrescu | Resident Evil Village
(3) Press pagedown a couple more times.

ACTUAL RESULTS: Lady Dimitrescu's photo keeps on reappearing at or near the top of my scrollport. And if I scroll up (with e.g. uparrow), it looks like a bunch of blank space has been inserted between her and the previous text (Now, on to the winners!).

Comment 10

[Daniel Holbert [:dholbert]]

Calling this S2 since it makes this article pretty unusable/unreadable, and it seems to be a bug in an optimization that was not meant to impact user-perceivable behavior.

Comment 11

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1492538

Comment 13

[Pascal Chevrel:pascalc]

Daniel, do we have a potential fix for this bug? I am assuming that we probably won't have time to uplift a fix to 98, is that correct?

Comment 14

[Daniel Holbert [:dholbert]]

No fix or thorough diagnosis yet -- and correct, it's unlikely we'll have a fix for 98. (FWIW we've been shipping with this bug since Firefox 80; this seems to be a bug in an optimization that we shipped as part of that release. Hoping to fix this during the near future, though.)

Comment 15

[Beth Rennie [:beth] (she/her)]

:dholbert, Any update on this?

Comment 16

[Dennis Schubert [:denschub]]

Setting WebCompat Priority P2 for now: we don't have evidence of many sites breaking because of this, but where it breaks, it makes content inaccessible.

Comment 17

[Emilio Cobos Álvarez (:emilio)]

This seems to work for me now.

Comment 18

[Daniel Holbert [:dholbert]]

Yeah, works for me as well, using STR from comment 9. It even works in Nightly 2022-01-10 (the datestamp from comment 9). So possibly there was a site change here. Too bad; that might mean we're unable to investigate further / know-if-it's-still-a-problem.

Closing as WORKSFORME, but please reopen if anyone can still reproduce.