try as a normal user: [user@laptop:~]$ xhost local: non-network local connections being added to access control list [user@laptop:~]$ su ( AND NOT SU - ) Password: [root@laptop:~]$ mozilla -- Debian unstable || pub 1024D/CDD636B2 || Linux 2.6.0-test11 #1 Thu Nov 27 09:49:23 CET 2003 i686 GNU/Linux