I had to run the Webdriver scripts on a Firefox and I had to use a particular proxy to get access to the QA/Dev environment. Here is the code that you can use to change the proxy settings.

FirefoxProfile firefoxProfile = new FirefoxProfile();
firefoxProfile.setPreference("network.proxy.type", 1);
firefoxProfile.setPreference("network.proxy.http", "100.00.100.100");
firefoxProfile.setPreference("network.proxy.http_port", 80);
firefoxProfile.setPreference("network.proxy.ssl", "100.00.100.100");
firefoxProfile.setPreference("network.proxy.ssl_port", 80);
firefoxProfile.setPreference("network.proxy.no_proxies_on", "");
driver = new FirefoxDriver(firefoxProfile);

Make changes to the PROXY_HOST – “100.00.100.100″ and the PROXY_PORT – 80. The PROXY_PORT is an Integer and PROXY_HOST is a String.