c# generates JS to fill webform: how to verify it works?

as continuation to:

WebBrowser Control in a new thread

how to fill an external web form with c# application?

I want to fill a website (i.e. gmail) web-form. I thought to avoid the WebBrowser control overhead. I used JS. but the following code doesn't work (as the Navigation_completed handler is called too many times). How can I verify the following code works? Is there any faster way to do so ?

static void Main(string[] args)
{
    runBrowserThread(new Uri("h开发者_开发问答ttps://accounts.google.com/ServiceLogin?service=mail&passive=true&rm=false&continue=https%3A%2F%2Fmail.google.com%2Fmail%2F%3Fui%3Dhtml%26zy%3Dl&bsv=llya694le36z&ss=1&scc=1&ltmpl=default&ltmplcache=2&hl=iw&from=logout"));

}

private static void runBrowserThread(Uri url)
{
    var th = new Thread(() =>
    {
        var br = new WebBrowser();
        br.DocumentCompleted += browser_DocumentCompleted;
        br.Navigate(url);
          br.Navigate("javascript: void(document.getElementsByName('Email')[0].value = 'Name';document.getElementsByName('Passwd')[0].value = 'Pass'; document.getElementsByName('signIn')[0].click();)");                                
        Application.Run();
    });
    th.SetApartmentState(ApartmentState.STA);
    th.Start();
}

static void browser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
    var br = sender as WebBrowser;
    if (br.Url == e.Url)
    {
        Console.WriteLine("Natigated to {0}", e.Url);
      //  Application.ExitThread();   // Stops the thread
    }
}

TIA