Created attachment 121253 [details]
/usr/share/applications/kde-mimeapps.list after fixing PDF entry
The entries in /usr/share/applications/kde-mimeapps.list have "kde4-" prefix for all .desktop filenames.
PDF files when opened from the downloads list of Firefox, starts up Gimp instead of Okular which is the associated application set in KDE. On this machine, only KDE is installed (no other DE). Similar behaviour is seen when opening PDF files from Zotero.
xdg-open foo.pdf works as expected and brings up Okular.
This problem was fixed by editing /usr/share/applications/kde-mimeapps.list and deleting "kde4-" prefix for the .desktop filename for application/pdf entry.
Sorry, kde-settings is a Fedora distro-specific package providing distro-specific defaults. It does not come from upstream KDE. So please file this at https://bugzilla.redhat.com/ . Thanks in advance.