event.offsetX in Firefox

From a JQuery bug tracker page - a nice polyfill is this:

var offX  = (e.offsetX || e.pageX - $(e.target).offset().left);

.. where e is the event returned from a jquery event. Obviously, only if you've got Jquery already on your project, otherwise will have to do the offset() stuff manually.

Try layerX, layerY

var x = (e.offsetX === undefined) ? e.layerX : e.offsetX;
var y = (e.offsetY === undefined) ? e.layerY : e.offsetY;

FIDDLE

Unfortunately no solution worked for me.

I found a good implementation here:

var target  = e.target || e.srcElement,
              rect    = target.getBoundingClientRect(),
              offsetX = e.clientX - rect.left,
              offsetY  = e.clientY - rect.top;

e.offsetX   = offsetX;
e.offsetY   = offsetY;

Unfortunately offsetX and layerX are not exactly the same as offsetX is the offset within the current element but layerX is the offset from the page. Below is a fix I am currently using for this:

function fixEvent(e) {
    if (! e.hasOwnProperty('offsetX')) {
        var curleft = curtop = 0;
        if (e.offsetParent) {
           var obj=e;
           do {
              curleft += obj.offsetLeft;
              curtop += obj.offsetTop;
           } while (obj = obj.offsetParent);
        }
        e.offsetX=e.layerX-curleft;
        e.offsetY=e.layerY-curtop;
    }
    return e;
}