Affected versions

• Nightly 80.0a1(20200722215545)
• 81.0a1 (20200729094932)

Affected platforms

• Windows 10x64

Steps to reproduce

1. Launch Firefox.
2. Go to https://www.reddit.com/.
3. Slowly scroll up and down through the page.

Expected result

• The content is properly rendered.

Actual result

• Certain content shakes on different areas of the website.

Regression range

• In bug 1523866, it was suggested that Regression window:
  https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=fbe6548db11ded24b5221180719ce66e785dc3c6&tochange=ad851d4345c08f7e0e5d5578652004194a6e667f

• Bug 1305957 seems to cause the regression.

Additional notes

• https://drive.google.com/file/d/11lI1WHbKZA94WX7u48X28DKgXmTkrPBb/view?usp=sharing - Screen cast of the issue

• https://drive.google.com/file/d/1yEuaZ6ezbAtLY3wbHi3yLRhf1sF_YmrF/view?usp=sharing - About:support raw data

• This issue does not have a clear repro rate or steps, it occurs randomly, but the issue is present.

• This issue was created as per comment 25 from issue 1523866.

• At the time of reproducing this issue I did not have fission.autostart and/or gfx.webrender.all prefs activated .

Can you confirm the issue doesn't happen with layout.css.scroll-anchoring.enabled=false? Otherwise it's likely a different issue.

Hello Emilio,

I have tried reproducing the issue with layout.css.scroll-anchoring.enabled=false and did not manage to encounter it. I have used 81.0a1(20200730093956) on an macOS 10.15.6 , Ubuntu 18 and Win10x64(same machine that first encountered the issue)

Triaging to S3, but if it were more frequently encountered or reproducible, I'd call it an S2. Sounds like it should block scroll-anchoring.

Quick question, does it stop after a bit? I would've expected the mitigations I added to stop scroll anchoring when we noticed there was no progress to help here.

And if (hopefully) so, there should be a warning on the web console... If so, what is it?

(In reply to Emilio Cobos Álvarez (:emilio) from comment #4)

Quick question, does it stop after a bit? I would've expected the mitigations I added to stop scroll anchoring when we noticed there was no progress to help here.

Hello,

Ever since the bug was created, I was unable to reproduce it anymore on latest Nightly and Beta builds.

When I did reproduce it, I only managed to reproduce the issue on random sections of the Feed and nowhere else.

I do not recall having any warning in browser console at that time. I will continue keeping an eye out for the issue as well as the web console and will return with my findings.