[x11] Error: cannot open display: localhost:0.0 - trying to open Firefox from CentOS 6.2 64bit and display on Win7

before start make sure of installation:

yum install -y xorg-x11-server-Xorg xorg-x11-xauth xorg-x11-apps
  1. start xming or cygwin
  2. make connection with X11 forwarding (in putty don't forget to set localhost:0.0 for X display location)
  3. edit sshd.cong and restart
     cat /etc/ssh/sshd_config | grep X
                             X11Forwarding yes
                             X11DisplayOffset 10
AddressFamily inet
  1. Without the X11 forwarding, you are subjected to the X11 SECURITY and then you must: authorize the remote server to make a connection with the local X Server using a method (for instance, the xhost command) set the display environment variable to redirect the output to the X server of your local computer. In this example: 192.168.2.223 is the IP of the server 192.168.2.2 is the IP of the local computer where the x server is installed. localhost can also be used.
blablaco@blablaco01 ~
$ xhost 192.168.2.223
192.168.2.223 being added to access control list

blablaco@blablaco01 ~
$ ssh -l root 192.168.2.223
[email protected] password:
Last login: Sat May 22 18:59:04 2010 from etcetc
[root@oel5u5 ~]# export DISPLAY=192.168.2.2:0.0
[root@oel5u5 ~]# echo $DISPLAY
192.168.2.2:0.0
[root@oel5u5 ~]# xclock&

Then the xclock application must launch.

Check it on putty or mobaxterm and don't check in remote desktop Manager software. Be careful for user that sudo in.