Hello Selva.

Some countries have stupid governments that are run by morons... oh, wait, that's not how it goes... Ahem... Some countries have national firewalls that block some domains. Be sure you don't live in one of them.

Still, you may be having a problem with some extension or plugin that is hindering your Firefox's normal behavior. Have you tried disabling all add-ons (just to check), to see if Firefox goes back to normal?

See also "Error_loading_some_websites": http://kb.mozillazine.org/Error_loading_websites

try change proxy once,then no proxy