class MyBrowser : WebBrowser
{
    protected override void WndProc(ref Message m)
    {
        const int WM_MOUSEMOVE = 0x0200;
        if (m.Msg == WM_MOUSEMOVE)
        {
            Debug.WriteLine("foo");
        }
        else base.WndProc(ref m);
    }
}

var browser = new WebBrowser
{
    Parent = this,
    Dock = DockStyle.Fill,
    ScriptErrorsSuppressed = true
};
browser.Navigate("yandex.ru");

var timer = new Timer();
timer.Tick += (o, e) =>
{
    if (browser.Document != null)
    {
        HtmlElement elem = browser.Document.GetElementFromPoint(browser.PointToClient(MousePosition));
        if (elem != null)
        {
            if (string.Compare(elem.TagName, "A", true) == 0)
                this.Text = elem.GetAttribute("href");
        }
    }
};
timer.Start();