时间到计时在ie显示正常，FF下无法显示

请高手帮忙，遇到这样一个问题：一个到计时代码在ie显示正常，在FF下无法显示时间数字。哪位高手能知道错误在哪里怎么修改吗？万分感谢！！代码如下：
<span id="span_dt_dt"></span> 
<SCRIPT language=javascript> function show_student163_time(){ window.setTimeout("show_student163_time()", 1000); 
BirthDay=new Date("12-21-2010 15:48:12"); 
today=new Date(); 
timeold=(BirthDay.getTime()-today.getTime()); 
sectimeold=timeold/1000 
secondsold=Math.floor(sectimeold); 
msPerDay=24*60*60*1000 
e_daysold=timeold/msPerDay 
daysold=Math.floor(e_daysold); 
e_hrsold=(e_daysold-daysold)*24; 
hrsold=Math.floor(e_hrsold); 
e_minsold=(e_hrsold-hrsold)*60; 
minsold=Math.floor((e_hrsold-hrsold)*60); 
seconds=Math.floor((e_minsold-minsold)*60); 
if(daysold<0)
{
daysold=0;
hrsold=0;
minsold=0;
seconds=0;
}
var daojishi="";
daojishi+="<table width=70 height=96 border=0 align=center cellpadding=0 cellspacing=0>"
daojishi+="<tr>"
daojishi+="<td width=112><span class=font7><b><font color=#009900>剩余时间</font></b></span></td>"
daojishi+="</tr>"
daojishi+="<tr>"
daojishi+="<td><span class=style1><b><font color=#000000>"+daysold+"天</font></b></span></td>"
daojishi+="</tr>"
daojishi+="<tr>"
daojishi+="<td><span class=style1><b><font color=#000000>"+hrsold+"小时</font></b></span></td>"
daojishi+="</tr>"
daojishi+="<tr>"
daojishi+="<td><span class=style1><b><font color=#000000>"+minsold+"分</font></b></span></td>"
daojishi+="</tr>"
daojishi+="</table>"
document.getElementById("span_dt_dt").innerHTML=daojishi ; 
} 
show_student163_time(); </SCRIPT>