Bug 508346

SUMMARY
When closing Falkon after a medium to long browsing session, I observe that the desktop completely freezes from a few seconds to several minutes (depending how long was the session and how many websites I visited). During the freeze, I notice the mouse is still responding, and Audacious is still playing music even though Audacious's window does not update.

The problem appeared at least with version 25.04, and is still present in 25.08.

I suspect that something is waiting (resource reclamation ?) in the thread handling the window closure, and blocks Kwin from doing other things. I observe the problem on the SteamDeck, and I haven't checked on other platforms. The fans of the SteamDeck do not go out of control during the desktop freeze, so I don't think the CPU is at 100% during the freeze.

STEPS TO REPRODUCE
1. Use Falkon for several minutes browsing websites.
2. Close Falkon

OBSERVED RESULT
The desktop is not responding and windows are not updating, from a few seconds to several minutes, depending on how much Falkon was used.

EXPECTED RESULT
Closing Falkon shouldn't cause desktop freezes.

OS VERSIONS
Linux/KDE Plasma: SteamOS 3.7.13 : 20250630.1
KDE Plasma Version: 6.2.5
KDE Frameworks Version: 6.9.0 
Qt Version: 6.8.1
Graphical platform : X11
Hardware : SteamDeck

APPLICATION VERSIONS
Falkon installed from FlatHub through the Discover application.
Falkon Version : 25.08.0
QtWebEngine Version : 6.9.0