HtmlElement jsElement = webBrowser1.Document.CreateElement("script");
jsElement.SetAttribute("type", "text/javascript");
jsElement.SetAttribute("text", "showMeAction = function(e) { window.alert(e);}");
webBrowser1.Document.Body.AppendChild(jsElement);

string[] args = new string[1];
args[0] = "Hello element!";
webBrowser1.Document.InvokeScript("showMeAction", args);

function createEvent(eventName, ofsx, ofsy)
{ 
  var evt = document.createEvent('MouseEvents'); 
  evt.initMouseEvent(eventName, true, false, null, 0, 0, 0, ofsx, ofsy, false, false, false, false, 0, null); 
  return evt; 
}
function moveElement(pxToMove)
{
var sliderKnob = document.getElementsByClassName("gt_slider_knob")[0]; 
var boxRect = sliderKnob.getBoundingClientRect();
var move = createEvent('mousemove', boxRect.left + sliderKnob.offsetLeft + pxToMove, boxRect.top + sliderKnob.offsetTop); 
var down = createEvent('mousedown', boxRect.left + sliderKnob.offsetLeft, boxRect.top + sliderKnob.offsetTop);
var up = createEvent('mouseup'); 
sliderKnob.dispatchEvent(down); 
document.dispatchEvent(move); 
sliderKnob.dispatchEvent(up); 
}