For visiting some special web sites or setting local DNS,you may need to use a proxy server in your web browser.This tutorial shows how to add proxy settings  for Opera and Firefox.

1.In firefox window,go to Edit->Preferences(or Tools->Options).Select Advanced->Network tab,click on Settings
proxy1


then,configure proxy settings in this window:
proxy11


2.For opera,go to Tools->Preferences.Advanced->Network tab,click on Proxy Settings


proxy2