2031961 - Unable to add tabs to old closed tab groups (tabGroupState.splitViews is undefined)

Status: VERIFIED FIXED

(Firefox :: Session Restore, defect, P1)

Description

[Nishchay [:nish]]

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:151.0) Gecko/20100101 Firefox/151.0

Steps to reproduce:

1. had a old closed tab group (is atleast 6-8 months old)
2. add a new tab to that closed tab group (right click on tab -> Add tab to tab group -> Closed Groups -> The old tab group

Actual results:

Uncaught TypeError: can't access property "push", tabGroupState.splitViews is undefined
addTabsToSavedGroup resource:///modules/sessionstore/SessionStore.sys.mjs:8530
addTabsToSavedGroup resource:///modules/sessionstore/SessionStore.sys.mjs:901
addTabsToSavedGroup chrome://browser/content/tabbrowser/tabbrowser.js:10934
<anonymous> chrome://browser/content/main-popupset.js:471
SessionStore.sys.mjs:8530:5
addTabsToSavedGroup resource:///modules/sessionstore/SessionStore.sys.mjs:8530
addTabsToSavedGroup resource:///modules/sessionstore/SessionStore.sys.mjs:901
addTabsToSavedGroup chrome://browser/content/tabbrowser/tabbrowser.js:10934
<anonymous> chrome://browser/content/main-popupset.js:471

https://searchfox.org/firefox-main/source/browser/components/sessionstore/SessionStore.sys.mjs#8530 apparently the old tab group doesn't have this new property "splitViews", so a backward incompatible change was pushed

Expected results:

add tab to tab group

Comment 1

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

:nsharpley, since you are the author of the regressor, bug 1995818, could you take a look? Also, could you set the severity field?

For more information, please visit BugBot documentation.

Comment 2

[Nishchay [:nish]]

some more info, reading my sessionstore.jsonlz4, i found that particular tab group was 'closedAt' : 1745741839853 (12 months ago)

while new tab groups have splitviews property,

{
"id": "1776241327834-50",
"name": "Example Closed Grp",
"color": "orange",
"collapsed": true,
"saveOnWindowClose": true,
"closedAt": 1776241410077,
"sourceWindowId": "window0",
"tabs": []
"splitViews": [],
"saved": true
}

old ones are like:

{
"id": "1745602415606-12",
"name": "old tab grp",
"color": "purple",
"collapsed": true,
"saveOnWindowClose": true,
"closedAt": 1745741839853,
"sourceWindowId": "window0",
"tabs": []
"saved": true
}

Comment 3

[Nishchay [:nish]]

Attachment: Bug 2031961 - Initialize tabGroupState.splitViews to prevent TypeError r=#sessionstore-reviewers

Older Tab groups don't have the property tabGroupState.splitViews leading to SessionStore.sys.mjs crashing when adding any new tab to these groups

Comment 4

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

Set release status flags based on info from the regressing bug 1995818

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/a49cf5708b53
https://hg.mozilla.org/integration/autoland/rev/a30396dec9ca
Initialize tabGroupState.splitViews to prevent TypeError r=sessionstore-reviewers,nsharpley

Comment 6

[Atila Butkovits]

https://hg.mozilla.org/mozilla-central/rev/a30396dec9ca

Comment 7

[Atila Butkovits]

https://hg.mozilla.org/mozilla-central/rev/a30396dec9ca

Comment 8

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

The patch landed in nightly and beta is affected.
:nish, 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.

Comment 9

[Nishchay [:nish]]

I can confirm that in nightly Version 151.0a1 (2026-04-17) (64-bit) my old tab groups (that i have multiple of) now are able to add new tabs to them and the sessionstore.jsonlz4 is updating to have the new property splitViews which it didn't before...

The bug is quite annoying for people who have many old closed? tab groups, don't know if its needs an uplift though
(and i think i don't have permission to set it to wontfix)

Comment 10

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

Attachment: Bug 2031961 - Initialize tabGroupState.splitViews to prevent TypeError

Older Tab groups don't have the property tabGroupState.splitViews leading to SessionStore.sys.mjs crashing when adding any new tab to these groups

Original Revision: https://phabricator.services.mozilla.com/D294570

Comment 11

[Phabricator Automation]

firefox-release Uplift Approval Request

• User impact if declined/Reason for urgency: Unable to add tabs to closed tab groups from before this patch.
• Code covered by automated testing?: no
• Fix verified in Nightly?: yes
• Needs manual QE testing?: yes
• Steps to reproduce for manual QE testing: Before applying the patch, create and save a tab group. Apply the patch. Restore the session and attempt to add tabs to the saved tab group.
• Risk associated with taking this patch: low
• Explanation of risk level: Very low risk one line change.
• String changes made/needed?: N/A
• Is Android affected?: no

Comment 12

[Monica Chiorean]

I was able to reproduce the issue on Win11x64 using Firefox build 138.0.
Verified with same profile that on Win11x64 using Firefox build 151.0b1, issue is not reproducing.
Issue is not reproducing on Win11x64 using latest Nightly 152.0a1(20260421211246) using an upgrade from 139.0a1.

Comment 13

[Pulsebot]

https://github.com/mozilla-firefox/firefox/commit/c35bf7e1e346
https://hg.mozilla.org/releases/mozilla-release/rev/88a6cef97476

Comment 14

[Monica Chiorean]

Issue is not reproducing on Win11x64 using Firefox 150.0.1(20260427013024). Marking as fixed.