For console access, you still don't need the root password. SSH to your FreeNAS installation as root (either connect as root, or connect as an unprivileged user and su -). Run 'jls'. You'll get a listing of your jails, with numbers in the "JID" column. Then run 'jexec # tcsh', where # is the JID number of the virtualbox jail. You'll be inside the jail as the root user. You can then, if you choose, set up the root password (though there's really no reason to do so), and you can make whatever other changes you like.