1984823 - Firefox 142 crashes on launch with certain KDE window decorations

Status: VERIFIED FIXED

(Core :: Widget: Gtk, defect)

Description

[jw_bugzilla+mozilla]

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:142.0) Gecko/20100101 Firefox/142.0

Steps to reproduce:

Running under KDE Plasma (specifically 6.4.4, others may work)

Go to settings -> colours and themes -> window decorations -> configure titlebar buttons. Here, customise window decorations to have minimise, maximise, and close on both the left and right sides of the titlebar.

Attempt to launch Firefox 142 (issue not present in 141 under the same conditions).

Actual results:

Firefox immediately crashes.

Running in a terminal produces this error:
/usr/include/c++/15/array:210: constexpr std::array<_Tp, _Nm>::value_type& std::array<_Tp, _Nm>::operator [with _Tp = HeaderBarButtonType; long unsigned int _Nm = 3; reference = HeaderBarButtonType&; size_type = long unsigned int]: Assertion '__n < this->size()' failed.

This occurs in safe mode, and after a clean reinstall. Per https://forum.manjaro.org/t/firefox-immediately-crashes-on-manjaro-kde-std-array-headerbarbuttontype-assert-gcc-15-2-1/180877/32, this also occurs in Flatpak, though that is not my thread and so I cannot confirm this directly.

Expected results:

Firefox launches normally

Comment 1

[Francesco Lodolo [:flod]]

Do you see crashes in about:crashes?

Please attach to the bug the raw content of your about:support:

• Type about:support in the address bar, press enter.
• Click Copy raw data to clipboard.
• Come back to this bug, click the Attach new file button above your first comment.
• Paste the content from your clipboard, add a description and hit Submit at the bottom.

Comment 2

[jw_bugzilla+mozilla]

Attachment: Contents of about:support

Worth noting this is not quite in the crashing setup - cannot access the browser to collect this information with the window decorations as specified in the original problem.

Comment 3

[jw_bugzilla+mozilla]

I can see crashes in about:crashes, yes
I submitted one of them from the crash reporter when it occurred, but it seemed redundant to submit the rest.
Let me know if it would be helpful for me to do that anyway.

Comment 4

[Francesco Lodolo [:flod]]

Please add the link of one of them to the bug, there is a lot more info in the bug report.

Comment 5

[jw_bugzilla+mozilla]

https://crash-stats.mozilla.org/report/index/a19801b8-4e99-4ae4-8e91-f171f0250822

Comment 6

[Francesco Lodolo [:flod]]

Thanks, hopefully someone familiar with Linux can identify the problem.

Since you mention that it's working in 141 but broken in 142, could you try running mozregression?
https://mozilla.github.io/mozregression/quickstart.html

You don't need to use the GUI or know the dates, mozregression --good 141 --bad 142 should work.

Comment 7

[jw_bugzilla+mozilla]

I'll take a look, though no guarantees

For what it's worth on the Linux front, I've also submitted the issue to KDE here: https://bugs.kde.org/show_bug.cgi?id=508643, though I assume the change is with Firefox since KDE didn't see any updates at the time the issue manifested.

Comment 8

[jw_bugzilla+mozilla]

mozregression result: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=4d59cfbe242a7f06027ea6a091d478c1c4d909df&tochange=4babe9a8ba89e0f20dad57c035f8575e489fa52f

One of the changes listed is about window decorations, so seems like a promising sign

Comment 9

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

:emilio, since you are the author of the regressor, bug 1972853, could you take a look? Also, could you set the severity field?

For more information, please visit BugBot documentation.

Comment 10

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1984823 - Fix decoration layout setting parsing. r=stransky

The break only broke of the inner loop, so if we find three decorations
on the left, and some after we trivially crashed.

Comment 11

[Emilio Cobos Álvarez [:emilio]]

Comment on attachment 9508969 [details]
Bug 1984823 - Fix decoration layout setting parsing. r=stransky

Beta/Release Uplift Approval Request

• User impact if declined/Reason for urgency: Startup crash in some rare configurations.
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: Yes
• If yes, steps to reproduce: comment 0
• List of other uplifts needed: none
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Trivial fix.
• String changes made/needed: none
• Is Android affected?: No

Comment 12

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

Set release status flags based on info from the regressing bug 1972853

Comment 14

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/e07c406c7d77
https://hg.mozilla.org/integration/autoland/rev/a3fbee6ffe8f
Fix decoration layout setting parsing. r=stransky

Comment 15

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/a3fbee6ffe8f

Comment 16

[Ryan VanderMeulen [:RyanVM]]

Comment on attachment 9508969 [details]
Bug 1984823 - Fix decoration layout setting parsing. r=stransky

Approved for 143.0b5.

Comment 17

[Pulsebot]

https://github.com/mozilla-firefox/firefox/commit/eab95b65ce1d
https://hg.mozilla.org/releases/mozilla-beta/rev/542fa08a503f

Comment 18

[Dianna Smith [:diannaS]]

Comment on attachment 9508969 [details]
Bug 1984823 - Fix decoration layout setting parsing. r=stransky

Approved for 142.0.1

Comment 19

[Pulsebot]

https://github.com/mozilla-firefox/firefox/commit/e4f4b93b596e
https://hg.mozilla.org/releases/mozilla-release/rev/a106d8cf5362

Comment 20

[Simona Badau, Desktop QA]

I was able to reproduce a crash using Firefox 142 on Ubuntu 25.04 with KDE Plasma 6.3.4 by configuring titlebar buttons on both sides. However, the crash signature I get differs from the one originally reported. Mine is here:
https://crash-stats.mozilla.org/report/index/8bcc74e7-b966-4aad-8dca-4befb0250827

I can confirm that the crash does not occur with the configured titlebar buttons on the latest Nightly 144.0a1 (Build ID: 20250826095322) and on Firefox 142.0.1.

@Emilio: Given the crash signature is different but there is no crash with the configured titlebar buttons, can this bug be considered as QA verified?

Comment 21

[Emilio Cobos Álvarez [:emilio]]

Yes, the signature depends on your distro, but it's the same crash.

Comment 22

[Simona Badau, Desktop QA]

Thank you, Emilio!

Based on Comments 21 and 22, setting the tracking flags for firefox142 and firefox144 to verified.

Comment 23

[Simona Badau, Desktop QA]

Verified as fixed using Firefox 143.0b5 on Ubuntu 25.04 and KDE Plasma 6.3.4.