Where is the mouse, Get mouse position cross browser

function whereIsMouse(e) {
	var posx = 0;
	var posy = 0;
	if (!e) var e = window.event;
	if (e.pageX || e.pageY) 	{
		posx = e.pageX;
		posy = e.pageY;
	}
	else if (e.clientX || e.clientY) 	{
		posx = e.clientX + document.body.scrollLeft
			+ document.documentElement.scrollLeft;
		posy = e.clientY + document.body.scrollTop
			+ document.documentElement.scrollTop;
	}
 
	return {'x': posx, 'y':posy};
}

Reference

Copied from quirksmode.org mouse events
http://www.quirksmode.org/js/events_properties.html
Check that page for updates in future for cross browser.