When shutting down the computer through the OS, Firefox closes each window separately instead of quitting (e.g. with Ctrl+Q). Windows with multiple tabs ask for confirmation, stopping or delaying the shutdown process, and single tab windows close and are not restored. I have to manually quit Firefox before shutting down the computer every time if I want my session to be correctly restored.

I have been using Firefox for a long time, and remember it working nicely with shutdown/logout. This issue showed up after changing my OS, so I believe it must be related to Flatpak, Fedora, KDE, or a mix of them.