Hi Kai,
Following script help me to double click with Webdriver (hope it will
help you)
if (document.createEventObject){
return arguments[0].fireEvent('ondblclick');
}else{
var evt = arguments[0].ownerDocument.createEvent('MouseEvents');
evt.initMouseEvent('dblclick',true,true,
element.ownerDocument.defaultView,1,0,0,0,0,false,
false,false,false,1,null);
return !element.dispatchEvent(evt);