tell your network settings the dns servers of your isp. Rather than just pointing it at your router
Cant tell you how to do it in centos unfortunately.

I can agree that Noscript was not configured. But if I run FF on Centos 5.6 with same DSL lineon same computer without using "NoScript", the same works perfectly well.
Why should FF require No Script under Cent OS 6 ?

There is another development -- I did some research on this issue.
If I use Ubuntu 10.04, exactly same problem is there. If I use Ubuntu 10.10, everything in FF works perfectly.If I switch to Ubuntu 11.04, again the same problem is there.

I really fail to understand so many different behaviours of FF under same conditions of Hardware ( same computer ) , same DSL line with only difference of versions of OS.