/etc/xdg/ is in mythbuntu-default-settings 1.13.
This file is owned by root:root, with mode 0o755.
..
/etc/xdg/xdg-mythbuntu/
/etc/xdg/xdg-mythbuntu/Thunar/
/etc/xdg/xdg-mythbuntu/Thunar/thunarrc
/etc/xdg/xdg-mythbuntu/Thunar/volmanrc
/etc/xdg/xdg-mythbuntu/applications/
/etc/xdg/xdg-mythbuntu/applications/defaults.list
/etc/xdg/xdg-mythbuntu/autostart/
/etc/xdg/xdg-mythbuntu/autostart/xfce4-tips-autostart.desktop
/etc/xdg/xdg-mythbuntu/menus/
/etc/xdg/xdg-mythbuntu/menus/xfce-applications.menu
/etc/xdg/xdg-mythbuntu/xfce4/
/etc/xdg/xdg-mythbuntu/xfce4/xfconf/
/etc/xdg/xdg-mythbuntu/xfce4/xfconf/xfce-perchannel-xml/
/etc/xdg/xdg-mythbuntu/xfce4/xfconf/xfce-perchannel-xml/xfce4-desktop.xml
/etc/xdg/xdg-mythbuntu/xfce4/xfconf/xfce-perchannel-xml/xfce4-keyboard-shortcuts.xml
/etc/xdg/xdg-mythbuntu/xfce4/xfconf/xfce-perchannel-xml/xfce4-panel.xml
/etc/xdg/xdg-mythbuntu/xfce4/xfconf/xfce-perchannel-xml/xfce4-session.xml
/etc/xdg/xdg-mythbuntu/xfce4/xfconf/xfce-perchannel-xml/xfprint.xml
/etc/xdg/xdg-mythbuntu/xfce4/xfconf/xfce-perchannel-xml/xfwm4.xml
/etc/xdg/xdg-mythbuntu/xfce4/xfconf/xfce-perchannel-xml/xsettings.xml