If you installed kubuntu parallel to ubuntu, you might find that the default browser is set to konqueror and cursor theme is oxygen which cannot modified by “gnome-default-applications-properties” and “gnome-appearance-properties”.

To fix this, use Debian update-alternatives tool:
update-alternatives –config x-www-browser
update-alternatives –config x-cursor-theme

All configurable options are listed at /var/lib/dkpg/alternatives