why this code doesn't work in firefox?

[wgale025]

[HTML]

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dt d">
<html xmlns="http://www.w3.org/1999/xhtml">
<head><title>dr ag</title>
<style>
<!--.drag{position: relative;}
-->
</style>
<script language="JavaS cript">
String.prototyp e.inc=function( s){return this.indexOf(s) >-1?true:false}
var agent=navigator .userAgent
window.isOpr=ag ent.inc("Opera" )
window.isIE=age nt.inc("IE")&&! isOpr
window.isMoz=ag ent.inc("Mozill a")&&!isOpr&&!i sIE

var dragapproved=fa lse
var z,x,y,t1,t2
function move(){
var oEvent=null,oEl ement=null;
if(isMoz){
oEvent=argument s[0];
oElement=oEvent .target;
}else{
oEvent=window.e vent;
oElement=oEvent .srcElement;
}
if (oEvent.button= =1&&dragapprove d){
//z.style.pixelLe ft=temp1+oEvent .clientX-x
//z.style.pixelTo p=temp2+oEvent. clientY-y
z.style.pixelLe ft=t1+oEvent.cl ientX-x
z.style.pixelTo p=t2+oEvent.cli entY-y
return false
}}
function drags(){
var oEvent=null,oEl ement=null;
if(isMoz){
oEvent=argument s[0];
oElement=oEvent .target;
}else{
oEvent=window.e vent;
oElement=oEvent .srcElement;
}
if (oElement.class Name=="drag"){
dragapproved=tr ue
z=oElement;
t1=z.style.pixe lLeft
t2=z.style.pixe lTop
x=oEvent.client X
y=oEvent.client Y
document.onmous emove=move
}}
document.onmous edown=drags
document.onmous eup=new Function("draga pproved=false")
</script>
</head><body>
<img src="http://www.hongen.com/pc/homepage/javascript/sample/img/draw.jpg" class="drag"></body>
</html>

[/HTML]

it works in IE very well.

[pbmods]

it works in IE very well.

Fantastic. What does it do? And what doesn't it do in Firefox? Are you getting an error?