MATE

In case it gets corrupted some applications might be unable to start at all - to clean it simply delete directory ~/.config/dconf

Reason for this is application .desktop file missing MimeType specification. For example for me mplayer and thunderbird are not listed as choices for video and mail respectively. To fix this edit application's .desktop file (in /usr/local/share/applications directory, or in ~/.local/share/applications) and run update-desktop-database afterwards (with -v to show its warnings).

One place to put all little tweaks to make it work better with FreeBSD.