Firefox's "Open folder" opens Gwenview

Solution 1:

On Kde, a different approach not involving direct editing. Took it from the link Miguel Aguayo gave in his answer. Someone attached that answer at the bottom in 2014.

1. Go to System Settings.
2. Open File Associations.
3. Go to Inode -> Directory
4. Remove Gwenview from the Application preference order list. Press Apply.
5. Optionally, you can add again Gwenview and make it at the bottom of the list of preferences.

Solution 2:

This link worked for me.

In short, in the file /home/$USER/.local/share/applications/mimeapps.list add these lines:

[Added Associations]

x-directory/normal=kde4-dolphin.desktop;kde4-kfmclient_dir.desktop;
inode/directory=kde4-dolphin.desktop;kde4-kfmclient_dir.desktop;kde4-gwenview.desktop;kde4-filelight.desktop;kde4-cervisia.desktop;

[Default Applications]

inode/directory=kde4-dolphin.desktop;kde4-kfmclient_dir.desktop;kde4-gwenview.desktop;kde4-filelight.desktop;kde4-cervisia.desktop;
x-directory/normal=kde4-dolphin.desktop;kde4-kfmclient_dir.desktop;