1977243 - Double splitter when tabs overflowing in vertical tabs mode

Status: VERIFIED FIXED

(Firefox :: Sidebar, defect, P3)

Description

[[:userChrome.css]]

Attachment: overflow.png

Steps to reproduce:

Enable vertical tabs.
Disable "Expand sidebar on hover" if enabled.
Add enough tabs to overflow.

Actual results:

There are two splitters, one after another.

• One is #sidebar-tools-and-extensions-splitter which is 2px tall.
• The other one is overflow 1px tall #tabbrowser-tabs[orient="vertical"][overflow]::after

This doesn't happen when "Expand sidebar on hover" is enabled.

Comment 1

[[:userChrome.css]]

Attachment: resizing.png

Comment 2

[Alin Ilea, Desktop Test Engineering]

Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:140.0) Gecko/20100101 Firefox/140.0

Hi,

I am able to reproduce this in beta 141 and nightly 142, but not on release 140, using Windows 10. Mozregression points to bug 1954155 as the regressor.
@Kelly, when you get a chance, could you please take a look over this one?

Thanks for the report!

Comment 3

[BugBot [:suhaib / :marco]]

Set release status flags based on info from the regressing bug 1954155

Comment 4

[BugBot [:suhaib / :marco]]

:kcochrane, since you are the author of the regressor, bug 1954155, could you take a look?

For more information, please visit BugBot documentation.

Comment 5

[BugBot [:suhaib / :marco]]

Set release status flags based on info from the regressing bug 1954155

Comment 6

[Kelly Cochrane [:kcochrane]]

Attachment: Bug 1977243 - Don't show bottom border for new tab button when vertical tabs are overflowing and the tools/extensions splitter is also showing

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/f2b48b5f6406
https://hg.mozilla.org/integration/autoland/rev/39dfe3ec11ec
Don't show bottom border for new tab button when vertical tabs are overflowing and the tools/extensions splitter is also showing r=tabbrowser-reviewers,sidebar-reviewers,nsharpley

Comment 8

[Cristian Tuns]

https://hg.mozilla.org/mozilla-central/rev/39dfe3ec11ec

Comment 9

[BugBot [:suhaib / :marco]]

The patch landed in nightly and beta is affected.
:kcochrane, is this bug important enough to require an uplift?

• If yes, please nominate the patch for beta approval.
  • See https://wiki.mozilla.org/Release_Management/Requesting_an_Uplift for documentation on how to request an uplift.
• If no, please set status-firefox142 to wontfix.

For more information, please visit BugBot documentation.

Comment 10

[Dana Lucaci, Desktop QA]

Reproduced with Firefox 142.0a1 (2025-07-14) on macOS 15.
Verified as fixed with Firefox 144.0a1 (20250825155516) and Firefox 143.0b4 (20250825091315) on macOS 14, Windows 10 and Ubuntu 22.