Passing username and password with proxy for Firefox Driver[Selenium] not working

FirefoxProfile profile = new FirefoxProfile();
Proxy firefox_proxy = new Proxy();
firefox_proxy.HttpProxy = proxy;
firefox_proxy.SslProxy = proxy;
profile.SetProxyPreferences(firefox_proxy);

Firefoxdriver driver = new FirefoxDriver(new FirefoxBinary(), profile, TimeSpan.FromMinutes(3));
driver.Navigate().GoToUrl("http://" + proxy_username + ":" + proxy_password + "@www.xyz.com/");

String PROXY = "localhost:8080";

org.openqa.selenium.Proxy proxy = new org.openqa.selenium.Proxy();
proxy.setHttpProxy(PROXY)
     .setFtpProxy(PROXY)
     .setSslProxy(PROXY);
DesiredCapabilities cap = new DesiredCapabilities();
cap.setCapability(CapabilityType.PROXY, proxy);
WebDriver driver = new FirefoxDriver(cap);