1930342 - Scroll anchoring causing flickering in rapidly changing elements

Status: UNCONFIRMED

(Core :: Layout: Scrolling and Overflow, defect)

Description

[vyn33r]

Attachment: Test page

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:131.0) Gecko/20100101 Firefox/131.0

Steps to reproduce:

A few months ago I noticed strange behavior in a chat room ( https://chat.destiny.gg/ ): occasionally, usually whenever the chat was moving particularly quickly, the messages would flicker for a split second. After recording the issue and slowing down the footage, the issue turned out to be scrolling related: sometimes the last message would jump a few pixels up, before going back to its intended position.

A week ago I got an issue on my own repository ( https://github.com/vyneer/orvods-go/issues/38 ) complaining about the same exact problem, just quite a bit worse. After poking around for a bit, I figured out that the problem seemed to disappear when the overflow-anchor property was set to none on the affected element.

I'm including a test page where you can observe the issue yourself and video of the bug happening on the previously mentioned pages, including the test one.

Video:

1. chat.destiny.gg flicker 1 - https://files.catbox.moe/quupfj.mp4
2. chat.destiny.gg flicker 2 - https://files.catbox.moe/s0e86d.mp4
3. vyneer.me flicker - https://files.catbox.moe/0oq6pc.mp4
4. test page flicker - https://files.catbox.moe/oisxvx.mp4

Steps to reproduce:

1. Open the provided test page
2. Click Start
3. Wait until the number of elements reaches the limit
4. Observe the "flicker"

I cannot observe the issue in Chrome 130.0.6723.69.

The issue does not affect Firefox 124, but affects version 125 and up. Mozregression gave me this pushlog URL: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=c5ec87ff79c5e8faf3e69f4dd3057c1df36c49e7&tochange=8be226e74ca568d032522bbdc3986658d66fdd9d

Thank you!

Actual results:

Scrollable element flickers as the contents get updated

Expected results:

Scrollable element does not flicker

Comment 1

[vyn33r]

Attachment: Flicker being observed on destiny.gg 1

Comment 2

[vyn33r]

Attachment: Flicker being observed on destiny.gg 2

Comment 3

[vyn33r]

Attachment: Flicker being observed on the test page

Comment 4

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

Setting Regressed by field after analyzing regression range found by mozregression in comment #0.

Comment 5

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

:hiro, since you are the author of the regressor, bug 1871760, could you take a look? Also, could you set the severity field?

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