winform webBrowser2.ScriptErrorsSuppressed = true;

1. _currentWeb.LoadCompleted += _currentWeb_LoadCompleted;

        private void _currentWeb_LoadCompleted(object sender, System.Windows.Navigation.NavigationEventArgs e)
        {
            var browser = sender as System.Windows.Controls.WebBrowser;

            if (browser == null || browser.Document == null)
                return;

            dynamic document = browser.Document;

            if (document.readyState != "complete")
                return;

            dynamic script = document.createElement("script");
            script.type = @"text/javascript";
            script.text = @"window.onerror = function(msg,url,line){return true;}";
            document.head.appendChild(script);
        }

2. 

FieldInfo fiComWebBrowser = typeof(WebBrowser)
        .GetField("_axIWebBrowser2",
                  BindingFlags.Instance | BindingFlags.NonPublic);
    if (fiComWebBrowser == null) return;
    object objComWebBrowser = fiComWebBrowser.GetValue(wb);
    if (objComWebBrowser == null) return;
    objComWebBrowser.GetType().InvokeMember(
        "Silent", BindingFlags.SetProperty, null, objComWebBrowser,
        new object[] { Hide });