Clicking file that doesn't have associated program is an annoying problem in KDE. It opens a window that can't be closed easily [even with sudo pkill].
STEPS TO REPRODUCE
- Download a file with no associated program installed through Firefox using
xdg-desktop-portal-kde. - Open it through the browser.
OBSERVED RESULT
An unclosable dialog will open with no suggestions. The "Show More" button will help if a suitable program is installed but not set, but it won't if you'd have to install it manually. I've also tested and does not happen in chromium, it opens the same KIO dialog Dolphin does.
EXPECTED RESULT
Be able to close the dialog, install a suitable program elsewhere, and then try again.
ADDITIONAL INFORMATION
Also there's an horizontal scrollbar at all times, even though there is no content.
This should be fixed now with changes in Plasma 5.25. [ Source ]