HTML5 with jQuery – e.offsetX is undefined in Firefox

Try using layerX and layerY for Firefox and offsetX for other browser.

If event fired with jquery:

xpos = e.offsetX === undefined ? e.originalEvent.layerX : e.offsetX;
ypos = e.offsetY === undefined ? e.originalEvent.layerY : e.offsetY;

If event fired with javascript:

xpos = e.offsetX==undefined?e.layerX:e.offsetX;
ypos = e.offsetY==undefined?e.layerY:e.offsetY;