Need help with nsIDOMWindowUtils.sendMouseEvent

Hi,

I'm trying to simulate mouse click on some element through
sendMouseEvent() (I can't use element.dispatchEvent() for some
reasons).
I'm experiencing problems with passing correct parameters.
Say if I have a DOM element how can I find x,y for sendMouseEvent?

My current code is as follows:
function simulateClick(element) {
   // get nsIDOMWindowUtils from content window
   var win = element.ownerDocument.defaultView;
   var req = win.QueryInterface(Ci.nsIInterfaceRequestor);
   var utils = req.getInterface(Ci.nsIDOMWindowUtils);

   var pos = findElementPosition(element);
   var x = pos.x+win.scrollX, y = pos.y+win.scrollY;

   utils.sendMouseEvent("mousedown", x, y, 0, 1, 0);
   utils.sendMouseEvent("mouseup", x, y, 0, 1, 0);
}

function findElementPosition(element) {
    var e = element;
    var pos = {x: 0, y: 0};
    while (e) {
        var x = 0, y = 0, ee = e;
        while (ee) {
            x += ee.offsetLeft;
            y += ee.offsetTop;
            ee = ee.offsetParent;
        }
        pos.x += x;
        pos.y += y;
        e = e.ownerDocument.defaultView.frameElement;
    }

    pos.x += Math.round(element.offsetWidth/2);
    pos.y += Math.round(element.offsetHeight/2);

    return pos;
}


Thanks,
Denis