I've installed Fedora 23 (standard edition) and afterwards used the software manager to install KDE 5. Under KDE, I can't change the file associations, even though there are some weird settings, such as using gedit as the default program for HTML files.
Going into the File Associations settings, I can see that - for example - gedit is the first application in the order of open for text/html files, but if I try to change the order and click Apply, the order reverts to how it was before I begun.
I've looked in .local/share/applications/mimeapps.list and it looks to be in order - it has text/html=firefox.desktop;org.gnome.gedit.desktop;calibre-ebook-edit.desktop,...
The xdg-mime tool shows the same problem:
$ xdg-mime query default text/html
org.gnome.gedit.desktop
$ xdg-mime default firefox.desktop text/html
$ xdg-mime query default text/html
org.gnome.gedit.desktop
How can I find out what is broken?
