Can someone tell me why this script works in IE but not FF on 3.8

[ult1lar]

It's a cursor script. Works just fine on IE but not FF on VBulletin. Works fine in FF on a normal webpage. TIA

<div id="span0" style="position:absolute;visibility:hidden;"><img src="elch.gif"></div>
<div id="span1" style="position:absolute;visibility:hidden;"><img src="elch.gif"></div>
<div id="span2" style="position:absolute;visibility:hidden;"><img src="elch.gif"></div>
<div id="span3" style="position:absolute;visibility:hidden;"><img src="elch.gif"></div>
<div id="span4" style="position:absolute;visibility:hidden;"><img src="elch.gif"></div>
<div id="span5" style="position:absolute;visibility:hidden;"><img src="elch.gif"></div>
<div id="span6" style="position:absolute;visibility:hidden;"><img src="zuegel.gif"></div>
<div id="span7" style="position:absolute;visibility:hidden;"><img src="santaclaus.gif"></div>
<div id="span8" style="position:absolute;visibility:hidden;"> </div>
<script>

var step=8
var stepbasic=8
var numberofimages=8
var spacebetweenimgs=32
var x,y
var flag=0
var xpos=new Array()

var ns6=document.getElementById&&!document.all?1:0

for (i=0;i<=8;i++) {
xpos[i]=-100
}

var ypos=new Array()
for (i=0;i<=numberofimages;i++) {
ypos[i]=-100
}

function handlerMM(e) {
x = (document.layers || ns6) ? e.pageX : document.body.scrollLeft+event.clientX
y = (document.layers || ns6) ? e.pageY : document.body.scrollTop+event.clientY
flag=1
}

function initiatetracker() {
if (document.all) {
for (i=0; i<numberofimages; i++) {
var thisspan=eval("span"+(i)+".style")
thisspan.posLeft=xpos[i]
thisspan.posTop=ypos[i]
thisspan.visibility="visible"
}
makesnake()
}

if (ns6) {
for (i=0; i<numberofimages; i++) {
document.getElementById("span"+i).style.left=xpos[i]
document.getElementById("span"+i).style.top=ypos[i]
document.getElementById("span"+i).style.visibility ="visible"
}
makesnake()
}
if (document.layers) {
for (i=0; i<numberofimages; i++) {
var thisspan=eval("document.span"+i)
thisspan.left=xpos[i]
thisspan.top=ypos[i]
thisspan.visibility="visible"
}

makesnake()
}
}

function makesnake() {
if (flag==1 && document.all) {
for (i=numberofimages; i>=1; i--) {
xpos[i]=xpos[i-1]+spacebetweenimgs
ypos[i]=ypos[i-1]
}
xpos[0]=x+stepbasic
ypos[0]=y

for (i=0; i<numberofimages; i++) {
var thisspan = eval("span"+(i)+".style")
thisspan.posLeft=xpos[i]
thisspan.posTop=ypos[i]
}
}

if (flag==1 && ns6) {
for (i=numberofimages; i>=1; i--) {
xpos[i]=xpos[i-1]+spacebetweenimgs
ypos[i]=ypos[i-1]
}
xpos[0]=x+stepbasic
ypos[0]=y

for (i=0; i<numberofimages; i++) {
document.getElementById("span"+i).style.left=xpos[i]
document.getElementById("span"+i).style.top=ypos[i]
}
}

else if (flag==1 && document.layers) {
for (i=numberofimages; i>=1; i--) {
xpos[i]=xpos[i-1]+spacebetweenimgs
ypos[i]=ypos[i-1]
}
xpos[0]=x+stepbasic
ypos[0]=y

for (i=0; i<numberofimages; i++) {
var thisspan = eval("document.span"+i)
thisspan.left=xpos[i]
thisspan.top=ypos[i]
}
}
var timer=setTimeout("makesnake()",30)
}

if (document.layers){
document.captureEvents(Event.MOUSEMOVE);
}
document.onmousemove=handlerMM;
window.onload=initiatetracker
</script>