C# Selenium Firefox Set socks proxy with Auth

In C# I'm trying to set socks proxy with authentification in firefox.

This doesn't work

    Proxy proxy = new Proxy();
    proxy.SocksProxy = sProxyIP + ":" + sProxyPort;
    proxy.SocksUserName = sProxyUser;
    proxy.SocksPassword = sProxyPass;
    options.Proxy = proxy;
    _driver = new FirefoxDriver(service, options);

This doesn't work too

   profile.SetPreference("network.proxy.socks", sProxyUser + ":" + sProxyPass + "@" + sProxyIP + ":" + sProxyPort);
   profile.SetPreference("network.proxy.socks_port", sProxyPort);

How can I solve this?