Bug 508643

Summary:	Conflict between Firefox 142 and customised window decorations causing consistent crash
Product:	[Plasma] Breeze	Reporter:	jw_bugzilla
Component:	window decoration	Assignee:	Plasma Bugs List <plasma-bugs-null>
Status:	RESOLVED UPSTREAM
Severity:	crash	CC:	kwin-bugs-null, uhhadd
Priority:	NOR
Version First Reported In:	6.4.4
Target Milestone:	---
Platform:	Fedora RPMs
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description jw_bugzilla 2025-08-23 12:36:08 UTC

SUMMARY
When KDE window decorations are customised to appear on both ends of the titlebar, Firefox 142 crashes on launch.

STEPS TO REPRODUCE
1. Go to settings -> colours and themes -> window decorations -> configure titlebar buttons.
2. Ensure close, minimise, and maximise buttons appear on both ends (left and right) of the titlebar. Save changes.
3. Attempt to launch Firefox 142.

OBSERVED RESULT
Firefox immediately crashes. Running in terminal produces an error:

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


EXPECTED RESULT
Firefox launches normally

SOFTWARE/OS VERSIONS
KDE Plasma Version: 6.4.4
KDE Frameworks Version: 6.17.0
Qt Version: 6.9.1

ADDITIONAL INFORMATION
Also submitted as a bug for Firefox at https://bugzilla.mozilla.org/show_bug.cgi?id=1984823

Comment 1 jw_bugzilla 2025-08-25 16:07:53 UTC

Resolved as an issue with Firefox in the previously linked thread