1650719 - Scrolling about:config is jank

Status: VERIFIED FIXED

(Core :: Layout, defect)

Description

[Blake]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0

Steps to reproduce:

1. Go to about:config
2. Hit "Show All"
3. Grab the scrollbar and drag it down slightly

Actual results:

When dragging the scrollbar down slightly, it should only move down a few lines

Expected results:

When dragging the scrollbar down slightly, it shouldn't jump like it does

Comment 1

[Alin Ilea, Desktop QA]

Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0

Hi,

I have managed to reproduce this issue on Beta 79.0b6 and latest Nightly 80.0a1 (2020-07-09) using Windows 10. Not reproducible on Release 78.0.1.

Further, I will move this over to a component so developers can take a look over it. If this is not the correct component please feel free to change it to an appropriate one.

This is a regression, here is the pushlog:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=76bffd1b3c6ecdba621930c770c52aae6e6205cc&tochange=1004d422aedb5994f9f2949fd4a4c67bc89e22c7

Thanks for your report.

Comment 2

[Cameron McCormack (:heycam)]

mozregression narrows it further for me down to bug 1647871. Emilio, do you want to take a look?

Comment 3

[Emilio Cobos Álvarez (:emilio)]

Attachment: Bug 1650719 - Don't lose the rect offset from the composition bounds. r=kats,hiro

This offset was reset in one of the two codepaths of D80723, but turns
out it's important for same-origin documents that are also
root-content-documents, like about: pages in the parent process, which
happened to hit the codepath that did not reset it. :(

Comment 4

[Emilio Cobos Álvarez (:emilio)]

Comment on attachment 9165500 [details]
Bug 1650719 - Don't lose the rect offset from the composition bounds. r=kats,hiro

Beta/Release Uplift Approval Request

• User impact if declined: Some internal pages that run in the parent process would jump when scrolling.
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: Yes
• If yes, steps to reproduce: comment 0
• List of other uplifts needed: none
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): One-liner that restores pre-existing behavior.
• String changes made/needed: none

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/9c57e70c264d
Don't lose the rect offset from the composition bounds. r=kats

Comment 6

[Narcis Beleuzu [:NarcisB]]

https://hg.mozilla.org/mozilla-central/rev/9c57e70c264d

Comment 7

[Alin Ilea, Desktop QA]

Verified - Fixed in latest Nightly 80.0a1 (build id: 20200723095657) using Windows 10 and Ubuntu 18.04.

Comment 8

[Julien Cristau [:jcristau]]

Comment on attachment 9165500 [details]
Bug 1650719 - Don't lose the rect offset from the composition bounds. r=kats,hiro

80 ships next week, and there are no plans for a 79 dot release