下面这段javascript在IE下能work, FF下不行，怎么修改

JScript code:
<script language="javascript">
function getPrice(id)
{
var item_danjia = document.all.item("danjia"+id);
var item_shuliang = document.all.item("shuliang"+id);
var item_zongjia = document.all.item("zongjia"+id);
var danjia = parseInt(item_danjia.innerHTML);
if(isNaN(item_shuliang.value)){
alert("Please input digital!");
shuliang.value = "";
item_zongjia.innerHTML = "";
}
if(item_shuliang.value==""){
item_zongjia.value = "";
}else{
var sl = parseInt(item_shuliang.value);
var zj = parseFloat(danjia*sl);
item_zongjia.innerHTML = String(zj);
}
}
</script>


HTML code:

<table cellspacing="0" cellpadding="0" border="0" width = "600">
<tr >
<th ><b>Products</b></th>
<th style="text-align:center;"><b>Qty</b></th>
<th>Price</th>
<th>Copy</th>
<th>Cost</