请问这段select联动的代码错在哪里？

[huaiping]

<script language="javascript">
var city=new Array();
var i=0;

city[0]=new Array("1","1","南宁");
city[1]=new Array("1","2","梧州");
city[2]=new Array("2","3","广州");
city[3]=new Array("3","4","长沙");

function chgprovince(ID){
document.f1.s2.length=0;
document.f1.s2.options[0]=new Option("--请选择--","0");
for(i=0;i<city.length;i++){
if(city[i][0]==ID){
document.f1.s2.options[document.f1.s2.length]=new Option(city[i][2],city[i][1]);
}
}
}
</script>
<form id="f1" name="form1" method="post" action="search.php">
<select name="s1" onchange="chgprovince(this.value);">
<option value="0">--请选择--</option>
<option value="1">广西</option>
<option value="2">广东</option>
<option value="3">湖南</option>
</select>
<select name="s2">
<option value="0">--请选择--</option>
</select>
</form>

[huaiping]

忘了说了，在 IE8 下正常，在 Firefox 3.5下没有反应。