Schneeflocken-Skript funktioniert nur im IE,nicht im Firefox

<SCRIPT>




Amount=22; //Smoothness! depends on image file size, the smaller the size the more you can use!


//Pre-load your image below!
Image0=new Image();
Image0.src="XMas/flake1.gif";
Image1=new Image();
Image1.src="XMas/flake2.gif";
Image2=new Image();
Image2.src="XMas/flake3.gif";
Image3=new Image();
Image3.src="XMas/flake4.gif";
Image4=new Image();
Image4.src="XMas/flake5.gif";
Image5=new Image();
Image5.src="XMas/flake6.gif";
Image6=new Image();
Image6.src="XMas/flake7.gif";
Image7=new Image();
Image7.src="XMas/flake8.gif";


grphcs=new Array(5)
grphcs[0]="XMas/flake1.gif"
grphcs[1]="XMas/flake2.gif"
grphcs[2]="XMas/flake3.gif"
grphcs[3]="XMas/flake4.gif"
grphcs[4]="XMas/flake5.gif"
grphcs[5]="XMas/flake6.gif"
grphcs[6]="XMas/flake7.gif"
grphcs[7]="XMas/flake8.gif"


Ypos=new Array();
Xpos=new Array();
Speed=new Array();
Step=new Array();
Cstep=new Array();
ns=(document.layers)?1:0;
if (ns){
for (i = 0; i < Amount; i++){
var P=Math.floor(Math.random()*grphcs.length);
rndPic=grphcs[P];
document.write("<LAYER><img></LAYER>");
}
}
else{
document.write('<div><div>');
for (i = 0; i < Amount; i++){
var P=Math.floor(Math.random()*grphcs.length);
rndPic=grphcs[P];
document.write('<img>');
}
document.write('</div></div>');
}
WinHeight=(document.layers)?window.innerHeight:window.document.body.clientHeight;
WinWidth=(document.layers)?window.innerWidth: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()*3+2;
 Cstep[i]=0;
 Step[i]=Math.random()*0.1+0.05;
}
function fall(){
var WinHeight=(document.layers)?window.innerHeight:window.document.body.clientHeight;
var WinWidth=(document.layers)?window.innerWidth:window.document.body.clientWidth;
var hscrll=(document.layers)?window.pageYOffset:document.body.scrollTop;
var wscrll=(document.layers)?window.pageXOffset:document.body.scrollLeft;
for (i=0; i <Amount> WinHeight){
Ypos[i]=-60;
Xpos[i]=Math.round(Math.random()*WinWidth);
Speed[i]=Math.random()*5+2;
}
if (ns){
document.layers['sn'+i].left=Xpos[i];
document.layers['sn'+i].top=Ypos[i]+hscrll;
}
else{
si[i].style.pixelLeft=Xpos[i];
si[i].style.pixelTop=Ypos[i]+hscrll;
} 
Cstep[i]+=Step[i];
}
setTimeout('fall()',50);
}
//-->
fall();
</SCRIPT>