2063789 - Split views in collapsed groups disappear after restoring session or dragging the groups

Status: VERIFIED FIXED

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

Description

[Merci chao]

Attachment: 2026_08_15_12_58_20.mp4

Since the recently added mechanism using the hidden attribute for split views, the split views inside collapsed groups are incorrectly marked as hidden when restoring a session. As a result, those split views disappear instead of being restored properly.

Steps to Reproduce:

1. Create a group with split views and tabs.

2. Collapse the group.

3. Close the window.

4. Restore the window.

5. Observe that the split views inside the collapsed group are missing, incorrectly marked as [hidden].

Comment 1

[Merci chao]

Attachment: 2026_08_17_11_24_01.mp4

Split views within a collapsed group also disapeared after moving the group.

Comment 2

[BugBot [:suhaib / :marco]]

:kpatenio, since you are the author of the regressor, bug 2038951, could you take a look? Also, could you set the severity field?

For more information, please visit BugBot documentation.

Comment 3

[Stephen Thompson [:sthompson]]

The tabsplitview is hiding itself if its constituent tabs are not visible, but that's too broad: tabs in a collapsed tab group are not considered visible https://searchfox.org/firefox-main/rev/ad5db99e4d2e00e9b5db2700c69050d709c7f340/browser/components/tabbrowser/content/tab.js#218-224. We probably need to ensure that the tabsplitview only hides based on the hidden state of its tabs, not the visible state.

Comment 4

[Stephen Thompson [:sthompson]]

Attachment: Bug 2063789 - hide split views explicitly, not based on tab visibility r=sclements,kpatenio

One major logic change: no longer allow the non-active sibling in an active tab to be hidden. The current behavior means 1) we're showing a tabpanel for a hidden tab, and 2) the active tab is not visible in the tab strip. I think these violate important invariants we have elsewhere. I haven't fully tested this out against add-ons that make use of tab hiding.

Main architectural change: since Tabbrowser is the one currently responsible for hiding tabs (it provides the API functions and Tabbrowser modifies the hidden attribute directly on tabs already), I think it's reasonable to make Tabbrowser responsible for hiding the splitview instead of the splitview governing its own hidden state based on the state of its tabs.

Comment 5

[BugBot [:suhaib / :marco]]

Set release status flags based on info from the regressing bug 2038951

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/a2bea15c3bd3
https://hg.mozilla.org/integration/autoland/rev/1fe1ed301ea5
hide split views explicitly, not based on tab visibility r=sclements,kpatenio,tabbrowser-reviewers

Comment 7

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/1fe1ed301ea5

Comment 8

[Monica Chiorean]

I was able to reproduce the issue on Win11x64 using Firefox build 156.0a1(20260814214318).
Verified as fixed on Win11x64 using Firefox builds 158.0a1 and 156.0.

Comment 9

[BugBot [:suhaib / :marco]]

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

Comment 10

[Stephen Thompson [:sthompson]]

Should be fixed in 157 as well since it landed in 156 and verified in 156