Affected versions

• Firefox 85.0a1 (BuildId:20201214091023)
• Firefox 84.0 (BuildId;20201211215739) - Please note that the print.tab_modal.enabled pref is disabled by default.
• Firefox 85.0b2 (BuildId:20201215185920)

Affected platforms

• Windows 10 64bit

Unaffected platforms

• Ubuntu 20.04 64bit.
• macOS 10.15

Steps to reproduce

1. Launch Firefox.
2. Access the following webpage
3. Hit CTRL + P in order to open the print preview.
4. Hold the click on the down arrow button from the print preview’s vertical dropdown.

Expected result

• No UI issues are encountered after pressing the vertical scroll bar buttons.

Actual result

• Print preview glitches when clicking the vertical scrollbar buttons

Regression Range

• This seems to be a regression.
• Pushlog: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=5dc0cfd11b2215c75bdd10a395855586ca9b5199&tochange=f0a8a5a5f78baa5e246082b71c2c2f56759e0518
• Potential Regressor: Bug 1669861

Notes

• For further information please observe the attached screencast.
• [Suggested Severity] I think that S4 fits for this issue.

Hi Botond,

It seems that mozregression pointed out Bug 1669861 for causing this regression.

Can you please take a look?

Thank you!

Based on the similar symptoms, this is likely the same issue as bug 1682919. I'll start with that one as it has a reduced testcase, and once I have a fix I'll check if it fixes this too.

Confirmed that this is fixed by the patch in bug 1682919.