Similar to: https://support.mozilla.org/en-US/questions/1329194 https://support.mozilla.org/en-US/questions/1298089 In KDE 5.24.4, Linux. I started to have some issues with "Open containing folder" probably because I installed many Gnome apps which may cause bad configurations in my system. I suspect this cause this issue even though I don't really have gnome file manager: https://polywogsys.livejournal.com/309405.html "Gnome based file managers, Nemo/Caja/Nautilus provide the entry org.freedesktop.FileManager1. So it doesn't matter what you set as your default application for the filemanager mimetype - as per the freedesktop.org standard, firefox will always select a filemanager based on dbus (if it's there)" But because the mimetype points to "dolphin", I dont really have other explanation either: $ xdg-mime query default inode/directory org.kde.dolphin.desktop