problem with javascript in Mozila Firefox??????urgent help required

<SCRIPT LANGUAGE="JavaScript" type="text/javascript">

currentX = currentY = 0; // initialize global position-tracking variables
whichEl = null; // initialize global element-being-dragged variable

function grabEl() // function for onmousedown
{
whichEl = event.srcElement;

while (whichEl.id.indexOf("DRAG") == -1) {
whichEl = whichEl.parentElement;
if (whichEl == null) { return }
}

if (whichEl != activeEl) {
whichEl.style.zIndex = activeEl.style.zIndex + 1;
activeEl = whichEl;
}

whichEl.style.pixelLeft = whichEl.offsetLeft;
whichEl.style.pixelTop = whichEl.offsetTop;

currentX = (event.clientX + document.body.scrollLeft);
currentY = (event.clientY + document.body.scrollTop);
//document.write(currentX);

}

function moveEl() // function for onmousemove
{
if (whichEl == null) { return };

newX = (event.clientX + document.body.scrollLeft);
newY = (event.clientY + document.body.scrollTop);
distanceX = (newX - currentX);
distanceY = (newY - currentY);
currentX = newX;
currentY = newY;

whichEl.style.pixelLeft += distanceX;
whichEl.style.pixelTop += distanceY;
event.returnValue = false;
document.form1.hidden1.value=currentX;
document.form1.hidden2.value=currentY;
}

function dropEl() // function for onmouseup
{
whichEl = null;

}

document.onmousedown = grabEl;
document.onmousemove = moveEl;
document.onmouseup = dropEl;

I have used above code to drag and drop image in my application.
it is working properly in IE.But i m not getting this functionality in Mozila .
i am not getting the problem ,can anyone one help me to solve this problem?
please help me as soon as possible.
thank you in advance.