1994089 - When the vertical tab bar is narrow, pinned tabs under a tab being dragged become invisible

Status: UNCONFIRMED

(Firefox :: Sidebar, defect, P3)

Description

[6k64x4ma]

Attachment: image.webp

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:144.0) Gecko/20100101 Firefox/144.0

Steps to reproduce:

1. Turn on Vertical tabs.
2. Disable "Expand sidebar on hover".
3. Pin multiple tabs.
4. Narrow the tab bar until the pinned tabs form a single column.
5. Drag a pinned tab to reorder it.

Actual results:

The pinned tabs under a tab being dragged become invisible.

Expected results:

The tabs should remain visible.

Comment 1

[Monica Chiorean]

I am not able to reproduce the issue on Win11x64 using FF build 144.0 and 146.0a1.
6k64x4ma, does the problem still happen if you start Firefox in Safe Mode? (Safe Mode disables add-ons, extensions and themes, hardware acceleration and some JavaScript stuff in order to exclude some possible reasons for problems.) See https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode?
Thank you.

Comment 2

[6k64x4ma]

The issue still occurs in Safe Mode.
But strangely, to get a single column of pinned tabs, it seems I either need to set "browser.uidensity" to 1 or run Firefox through mozregression-gui.
FYI I can reproduce the issue with Nightly 20251015095022 via mozregression-gui with "browser.uidensity" left untouched.

Comment 3

[Sam Foster [:sfoster] (he/him)]

:nikkis, have you come across this? Can you triage it please?

Comment 4

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

Redirect a needinfo that is pending on an inactive user to the triage owner.
:sfoster, since the bug has recent activity, could you please find another way to get the information or close the bug as INCOMPLETE if it is not actionable?

For more information, please visit BugBot documentation.

Comment 5

[Sam Foster [:sfoster] (he/him)]

Wrong bugmail account for :nikkis. Lets try that again. See comment 3

Comment 6

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

Attachment: Screen Recording 2025-11-13 at 12.21.17 PM.mov

Comment 7

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

Apologies for the delay. I am able to reproduce it with the sidebar expanded but minimized to have only 1 pinned tab per row. When the sidebar is collapsed, moving pinned tabs works fine. See attached.