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

So, it turns out that X11 wasn't actually installed on the centOS. There didn't seem to be any indication anywhere of it not being installed. I did the following command and now firefox opens:

yum groupinstall 'X Window System' 

Hope this answer will help others that are confused :)

I faced this issue once and was able to resolve it by fixing of my /etc/hosts. It just was unable to resolve localhost name... Details are here: http://itvictories.com/node/6

In fact, there is 99% that error related to /etc/hosts file

X server just unable to resolve localhost and all consequent actions just fails.

Please be sure that you have a record like

127.0.0.1 localhost

in your /etc/hosts file.