2006897 - Resizing views after they were resized and then reversed will show a blank space on the right side

Status: VERIFIED FIXED

(Firefox :: Tabbed Browser: Split View, defect, P1)

Description

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

Attachment: split_reverse_resize.gif

Found in

• 148.0a1 (2025-12-18)

Affected versions

• 148.0a1 (2025-12-18)
• 147.0b5

Tested platforms

• Affected platforms: Ubuntu 24, Windows 11, macOS 26
• Unaffected platforms: none

Steps to reproduce

1. Create a split view and resize it.
2. Use the Reverse Tabs option.
3. Resize the Split view and observe the right part of the browser.

Expected result

• No blank space is displayed.

Actual result

• A blank space will appear on the right side of the browser after resizing.

Regression range

• This is not a regression because it happens after the first reverse tabs implementation with bug 1986951

Additional notes

• Attached a screen recording.

Comment 1

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

The severity field is not set for this bug.
:dwalker, could you have a look please?

For more information, please visit BugBot documentation.

Comment 2

[Sarah Clements [:sclements]]

Jonathan can you take a look please? Looks like a similar issue to bug 2006834.

Comment 3

[Sarah Clements [:sclements]]

Bug 2006876 might also be related?

Comment 4

[Jonathan Sudiaman [:jsudiaman]]

Attachment: Bug 2006897 - Unset right panel width after reversing the order of a Split View. r?#tabbrowser-reviewers

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/acb7901c97f4
https://hg.mozilla.org/integration/autoland/rev/0dfa574aabb0
Unset right panel width after reversing the order of a Split View. r=tabbrowser-reviewers,mkennedy,nsharpley

Comment 6

[Serban Stanca [:SerbanS]]

https://hg.mozilla.org/mozilla-central/rev/0dfa574aabb0

Comment 7

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

The patch landed in nightly and beta is affected.
:jsudiaman, 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-firefox148 to wontfix.

For more information, please visit BugBot documentation.

Comment 8

[Donal Meehan [:dmeehan]]

Splitview is nightly only

Comment 9

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

Verified fixed with Firefox 149.0a1 (2026-01-14) on Windows 11, macOS 26 and Ubuntu 24. The blank space is no longer preserved after following the steps from comment 0.