1539443 - [Reddit] Page elements flash on fast scrolling

Status: NEW

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

Description

[Alexandru Trif, QA [:atrif]]

Affected versions

• Firefox 67.0b5 (20190325125126)
• Firefox 68.0a1 (20190327044526)
• Firefox 66.0.2 (20190326175229)

Affected platforms

• macOS 10.14
• Ubuntu 18.04 x64
• Windows 7 x64
• Windows 10 x64

Steps to reproduce

1. Open Firefox and go https://www.reddit.com/.
2. Drag the scrollbar or use touchpad to fast scroll up and down on the page.
3. Observe the behavior.

Expected result

• The scrolling is smooth without any visual glitches.

Actual result

• "Back to top" button flashes.
• The ADS section flashes as well.

Regression range

• Last good revision: 3119a9a0b5dee60ac77b7596ae5dbe0658f598ad (2016-12-27)
• First bad revision: d7b6af32811bddcec10a47d24bd455a1ec1836fc (2016-12-28)
• Pushlog:
  https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=3119a9a0b5dee60ac77b7596ae5dbe0658f598ad&tochange=d7b6af32811bddcec10a47d24bd455a1ec1836fc

Additional Notes

• On Chrome the advertisement doesn't flash on scroll, neither the "Back to top" button.
• The issue is more visible on macOS where the touchpad is used to fast scroll up and down.
• Attached a screen recording with the issue: link.

Comment 1

[Alexandru Trif, QA [:atrif]]

Updating summary and adding regression range.

Comment 2

[Jessie [:jbonisteel] pls NI]

Could this be APZ related, Kats?

Comment 3

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

Yeah this looks like it's another instance of bug 1424714.

Comment 4

[MarjaE]

Is this old or new reddit?

Reddit is currently undergoing a redesign, and the new design uses endless scrolling, so of course it's buggy.

I use my own font settings so I can read things, and sites which constantly load and unload elements end up flashing as they load elements based on their expected sizes, and then resize elements based on my sizes.

Comment 5

[Alexandru Trif, QA [:atrif]]

Hello, this is on new reddit. The issue doesn't apply on old one because on scrolling the ads don't follow on scrolling on the page. And "Back to top" button is not present there. I tried setting the page to display more content but still the presented behavior don't apply. Thank you!

Comment 6

[Patricia Lawless]

Bulk change of P3 carryover bugs to wontfix for 68.

Comment 7

[Liz Henry (:lizzard Please n-i to RyanVM, jcristau, or pascal)]

Happy to take a patch for 70 but since this is triaged and set to P3 priority I'm setting it as fix-optional.
That will remove the bug from weekly regression triage.

Comment 8

[Botond Ballo [:botond]]

Alexandru, would you be able to re-test with a recent Nightly, to see if this was fixed by bug 1424714?

Comment 9

[Alexandru Trif, QA [:atrif]]

The flashes are still happening using the latest Nightly (20200422214848) on Windows 10x64. I made a screen recording: link.