You are not setting your Proxy server in the webBrowser1_Navigating event handler, only in your Form_Load event handler
Add the code to the
webBrowser1_Navigating event handler to make your HttpWebRequest use the Proxy
WebProxy myProxy = new WebProxy(proxyBox.Text);
myRequest.Proxy = myProxy;
In Form_Load you have created a HttpWebRequest & set the Proxy
In the WebBrowser Navigating event handler you have created another HttpWebRequest but have not set the proxy server..
Kind Regards