WebBrowser Control Redirection

I'm writing a C# application that requests Facebook authentication from the user.

To this end, I have created a WebBrowser control, and navigate to "https://www.facebook.com/dialog/oauth?client_id=YOUR_APP_ID&redirect_uri=https://www.facebook.com/connect/login_success.html".  This shows the authorization window to the user.  When the user clicks Allow, the browser is redirected (via HTTP 302) to "https://www.facebook.com/connect/login_success.html?code=ACCESS_CODE".  However, when the WebBrowser control is redirected to this URL, it disappears from its parent form and pops up in a new Internet Explorer window.

Why is this happening, and how can I fix it?

Relevant code:

public bool getAuthCode()
{
  Form f = new Form();
  WebBrowser wb = new WebBrowser();
  WebBrowserDocumentCompletedEventHandler handle = new WebBrowserDocumentCompletedEventHandler(wb_urlChange_Handler);
  wb.DocumentCompleted += handle;
  wb.Dock = DockStyle.Fill;
  f.Text = "Authenticate App";
  f.Size = new System.Drawing.Size(1000, 600);
  f.Controls.Add(wb);
  wb.Navigate(new System.Uri(this.generateAuthCodeURL()));
  f.ShowDialog();
  f.Dispose();
  return true;
}
private void wb_urlChange_Handler(object sender, WebBrowserDocumentCompletedEventArgs e)
{
  if (handleAuthCodeURL(e.Url.ToString()))
  {
	WebBrowser wb = (WebBrowser)sender;
	wb.Dispose();
	((Form)wb.Parent).Close();
  }
}