Coding difference between IE and firefox

I am using a code to have falling poppies on my forum for rememberance day...it it the falling leaves code, just with poppies instead of leaves

It works lovely in IE and chrome, but doesnt work in Firefox...you just get a few poppies stuck in the corner...please can someone help me, I dont understand why it works in one browser but not another

Code:

<script language="JavaScript1.2">

//Autumn leaves- by Kurt Grigg (kurt.grigg@virgin.net)
//Modified by Dynamic Drive for NS6 functionality
//visit http://www.dynamicdrive.com for this script

//Pre-load your image below!
grphcs=new Array(6)
Image0=new Image();
Image0.src=grphcs[0]="http://i961.photobucket.com/albums/ae96/leamarie75/6-1.png";
Image1=new Image();
Image1.src=grphcs[1]="http://i961.photobucket.com/albums/ae96/leamarie75/5-1.png"
Image2=new Image();
Image2.src=grphcs[2]="http://i961.photobucket.com/albums/ae96/leamarie75/4-1.png"
Image3=new Image();
Image3.src=grphcs[3]="http://i961.photobucket.com/albums/ae96/leamarie75/3-1.png"
Image4=new Image();
Image4.src=grphcs[4]="http://i961.photobucket.com/albums/ae96/leamarie75/2-1.png"
Image5=new Image();
Image5.src=grphcs[5]="http://i961.photobucket.com/albums/ae96/leamarie75/1-1.png"

Amount=8; //Smoothness depends on image file size, the smaller the size the more you can use!
Ypos=new Array();
Xpos=new Array();
Speed=new Array();
Step=new Array();
Cstep=new Array();
ns=(document.layers)?1:0;
ns6=(document.getElementById&&!document.all)?1:0;

if (ns){
for (i = 0; i < Amount; i++){
var P=Math.floor(Math.random()*grphcs.length);
rndPic=grphcs[P];
document.write("<LAYER NAME='sn"+i+"' LEFT=0 TOP=0><img src="+rndPic+"></LAYER>");
}
}
else{
document.write('<div style="position:absolute;top:0px;left:0px"><div style="position:relative">');
for (i = 0; i < Amount; i++){
var P=Math.floor(Math.random()*grphcs.length);
rndPic=grphcs[P];
document.write('<img id="si'+i+'" src="'+rndPic+'" style="position:absolute;top:0px;left:0px">');
}
document.write('</div></div>');
}
WinHeight=(ns||ns6)?window.innerHeight:window.document.body.clientHeight;
WinWidth=(ns||ns6)?window.innerWidth-70:window.document.body.clientWidth;
for (i=0; i < Amount; i++){                                                               
 Ypos[i] = Math.round(Math.random()*WinHeight);
 Xpos[i] = Math.round(Math.random()*WinWidth);
 Speed[i]= Math.random()*5+3;
 Cstep[i]=0;
 Step[i]=Math.random()*0.1+0.05;
}
function fall(){
var WinHeight=(ns||ns6)?window.innerHeight:window.document.body.clientHeight;
var WinWidth=(ns||ns6)?window.innerWidth-70:window.document.body.clientWidth;
var hscrll=(ns||ns6)?window.pageYOffset:document.body.scrollTop;
var wscrll=(ns||ns6)?window.pageXOffset:document.body.scrollLeft;
for (i=0; i < Amount; i++){
sy = Speed[i]*Math.sin(90*Math.PI/180);
sx = Speed[i]*Math.cos(Cstep[i]);
Ypos[i]+=sy;
Xpos[i]+=sx;
if (Ypos[i] > WinHeight){
Ypos[i]=-60;
Xpos[i]=Math.round(Math.random()*WinWidth);
Speed[i]=Math.random()*5+3;
}
if (ns){
document.layers['sn'+i].left=Xpos[i];
document.layers['sn'+i].top=Ypos[i]+hscrll;
}
else if (ns6){
document.getElementById("si"+i).style.left=Math.min(WinWidth,Xpos[i]);
document.getElementById("si"+i).style.top=Ypos[i]+hscrll;
}
else{
eval("document.all.si"+i).style.left=Xpos[i];
eval("document.all.si"+i).style.top=Ypos[i]+hscrll;
}
Cstep[i]+=Step[i];
}
setTimeout('fall()',20);
}

window.onload=fall
//-->
</script>

it work for me on firefox