Affected versions

• 84.0b1 (20201116212331)
• 85.0a1(20201116210217)

Affected platforms

• Windows 7x64

Steps to reproduce

1. Open Firefox and go to a login site (e.g Facebook/ Twitter).
2. Focus the page and the focus username field.

Expected result

• Dropdown is displayed as expected.

Actual result

• Dropdown is invisible. If not reproduced repeat to focus the page and username field.

Regression range

• Pushlog: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=6dcbbdb84c453149f460f6868eeb135d6622c57d&tochange=e9ac2e3b9176ddf3fa0949bd71da74e0518346d4

Notes

• Attached a screen recording.
• I cannot reproduce the issue on Windows 10x64, macOS 10.12 or Ubuntu 18.04.
• Note that the issue is intermittent.
• When hovered the dropdown menu is displayed as expected.
• The issue is not reproducible without WebRender.

Suggested Severity: S3

Jeff is going to see if he can repro this on a win7 machine. It should be easy enough to back out (and uplift to beta) if needed, it's a small isolated change. It is odd though, since in theory that change should have had no effect except removing a potential race condition.

:atrif, can you attach about:support to this bug?

I have Win7 PC and confirmed that I could reproduce the problem.

(In reply to Sotaro Ikeda [:sotaro] from comment #2)

:atrif, can you attach about:support to this bug?

Yes. Attaching here from two machines on which we were able to replicate the issue. If more information is needed please let me know. Thank you!

Looks like Sotaro can reproduce so I'm not going to try.

Sotaro, could you confirm if reverting the linked regressing patch does fix it? If so, let's just back that out of nightly and beta for now, until we have more time to investigate the root cause?

I tested with local build on win7 PC. And I confirmed that reverting the patch fixed the problem.

Without reverting it, local build caused the problem. With reverting it, I did not see the problem.

Bug 1675136 has been backed out from all affected branches. This should be fixed in 84.0b4.
https://hg.mozilla.org/integration/autoland/rev/dbe6164c7ebd
https://hg.mozilla.org/releases/mozilla-beta/rev/f62ddd62dddc

The issue is verified fixed with Firefox 85.0a1 (20201208213457) and 84.0 (20201207203640) on Windows 7x64. The drop-down password menus are correctly displayed on Facebook and Twitter.