STEPS TO REPRODUCE 1. Use Firefox 114 2. Set up multiple profiles 3. Load two profiles, each in a separate window 4. Hit Alt+Tilde on the keyboard OBSERVED RESULT The tabbox appears with only one window in it, as though KWin can't detect that the two Firefox windows are both instances of the same app EXPECTED RESULT Two windows appear in the Alt+Tilde tabbox, one per Firefox window SOFTWARE/OS VERSIONS Operating System: Fedora Linux 38 KDE Plasma Version: 5.27.80 KDE Frameworks Version: 5.240.0 Qt Version: 6.5.1 Kernel Version: 6.3.8-200.fc38.x86_64 (64-bit) Graphics Platform: wayland Processors: 8 × Intel® Core™ i7-10510U CPU @ 1.80GHz Memory: 15.2 GiB of RAM Graphics Processor: Mesa Intel® UHD Graphics ADDITIONAL INFORMATION - Does not occur if you just make a regular new window in Firefox with Ctrl+N - Does not occur with other multi-window apps like Dolphin - The Task Manager widget can correctly group the two windows from multiple Firefox profiles I'm pretty sure this didn't happen before, but I haven't isolated it to a particular version of Firefox or a KWin change.
Ah I found the trigger: this only happens when Firefox is running in XWayland mode. Running it in native Wayland mode resolves the issue and lets KWin identify both windows as belonging to the same app. The trigger for that happening was something unrelated in distro packaging.