2014334 - Split view does not show colored outline when used as a group target during dragging

Status: RESOLVED FIXED

(Firefox :: Tabbed Browser: Split View, defect, P3)

Description

[Merci chao]

Attachment: 2026_02_04_10_17_13.mp4

149.0a1 (2026-02-03)
When dragging a tab over a split view to group it, the split view does not display a colored outline to indicate that it is about to be grouped.

Comment 1

[Alexandru Trif, Desktop Test Engineering [:atrif]]

Confirming this with Firefox 149.0a1 (2026-02-03) on Windows 11 and macOS 26. Thank you!

Comment 2

[Nikki Sharpley (:nikkis) (she/her)]

To help Mozilla out with this bug, here's the steps:

1. Comment here on the bug that you want to volunteer to help.
   This will tell others that you're working on the next steps.
2. Download and build the Firefox source code
   • If you have any problems, please ask on
     Element/Matrix
     in the #introduction channel. They're there to help you get started.
   • You can also read the
     Firefox Contributors' Quick Reference,
     which has answers to most development questions.
3. Start working on this bug.
   • If you have any problems with this bug,
     please comment on this bug and set the needinfo flag for me.
     Also, you can find me and my teammates on the #sidebar channel on
     Element/Matrix
     most hours of most days.
4. Build your change with mach build and test your change with
   mach test browser/components/tabbrowser/test/browser.
   Also check your changes for adherence to our style guidelines by using mach lint
5. Submit the patch (including an automated test, if applicable) for review.
   Mark me as a reviewer so I'll get an email to come look at your code.
   • Getting your code reviewed
   • This is when the bug will be assigned to you.
6. After a series of reviews and changes to your patch,
   I'll mark it for checkin or push it to autoland.
   Your code will soon be shipping to Firefox users worldwide!
7. ...now you get to think about what kind of bug you'd like to work on next.
   Let me know what you're interested in and I can help you find your next contribution.

Comment 3

[Shloka Gupta]

Hi, would love to work on this!

Comment 4

[Noble Chinonso]

Hi, I want to help out with this bug

Comment 5

[konyhéa]

Hi, I'd like to volunteer to work on this bug.
I have already set up my local Firefox build and
am ready to start working on it.

Comment 6

[konyhéa]

I have reproduced the issue locally and confirmed that no colored outline appears on the tab-split-view-wrapper when dragging a tab over it to create a group.

The fix adds a CSS rule for tab-split-view-wrapper[dragover-groupTarget] using the existing --tab-dragover-outline-color variable and --tab-border-radius to stay consistent with the rest of the tab strip drag and drop visual feedback system.

Patch submitted for review on Phabricator:
https://phabricator.services.mozilla.com/D289104

Additional Finding:
While investigating this bug, I also noticed that the colored outline is missing in a second scenario — when dragging a tab over a split view wrapper that already belongs to an existing tab group (movingtab-addToGroup state). The current patch only addresses the initial grouping scenario as described in the bug. I wanted to flag this as a potential follow-up fix — should I include it in this patch, or would you prefer it as a separate bug?

Looking forward to your feedback!

Comment 7

[konyhéa]

Attachment: before screenshot

Comment 8

[konyhéa]

Attachment: after screen recording

Comment 9

[Merci chao]

Attachment: 2026_03_22_23_12_17.mp4

Honestly, I expect it to have the same look and feel as grouping with normal tabs, for consistency.

Comment 10

[konyhéa]

Thank you for the feedback. I will update the patch to match the same look and feel as normal tabs when being grouped.

Comment 11

[konyhéa]

Attachment: output.mp4

Please see the attached video demonstrating the updated behavior. Kindly confirm if this looks good so I can proceed with submitting the patch for review.

Comment 12

[Merci chao]

(In reply to konyhéa from comment #11)

Created attachment 9555888 [details]
output.mp4

Please see the attached video demonstrating the updated behavior. Kindly confirm if this looks good so I can proceed with submitting the patch for review.

Just in case, you may also want to check it in light theme. By the way, I’m not a member of the Firefox team, just a regular user, so it’s better to let the team confirm whether it’s good or not. I guess I just came here to report the bug and share some thoughts.

Comment 13

[Merci chao]

Attachment: Region.png

(In reply to konyhéa from comment #11)

Created attachment 9555888 [details]
output.mp4

Please see the attached video demonstrating the updated behavior. Kindly confirm if this looks good so I can proceed with submitting the patch for review.

1. In your screen recording, there’s a weird dark line under the upper outline. Maybe it’s just due to the video quality.
2. The separator in the split view doesn’t connect to the outline. I’m not sure how it’s supposed to be designed.

Comment 14

[konyhéa]

Attachment: Bug 2014334 - add outline to tab-split-view-wrapper when used as a drag group target

When dragging a tab over a tab-split-view-wrapper to group it, no colored outline was displayed to indicate that the split view was about to become a group target. This was because no CSS rule existed for tab-split-view-wrapper[dragover-groupTarget], unlike
individual tabs and tab group labels, which already had this visual feedback implemented.

This patch adds an outline to tab-split-view-wrapper when the dragover-groupTarget attribute is set during a drag operation, using the existing --tab-dragover-outline-color variable and --tab-border-radius to stay consistent with the rest of the tab strip drag and drop visual feedback system.

Comment 15

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/d418ae709360
https://hg.mozilla.org/integration/autoland/rev/5a92b7f57bed
add outline to tab-split-view-wrapper when used as a drag group target r=nsharpley,desktop-theme-reviewers,tabbrowser-reviewers

Comment 16

[amarc]

https://hg.mozilla.org/mozilla-central/rev/5a92b7f57bed

Comment 17

[BugBot [:suhaib / :marco/ :calixte]]

Since nightly and release are affected, beta will likely be affected too.
For more information, please visit BugBot documentation.

Comment 18

[BugBot [:suhaib / :marco/ :calixte]]

The patch landed in nightly and beta is affected.
:ndukaprincek, 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-firefox150 to wontfix.

For more information, please visit BugBot documentation.