我的这段js代码为什么在火狐用不了，求大牛

    <table border=0 align=center cellpadding=1 cellspacing=1 cellspace=0 >
<tr><td valign=top bgcolor=ffffff id=marquePic1>
    <table width='100%' border='0' cellspacing='0'>
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   </tr>
   </table></td>
   <td id=marquePic2 valign=top></td></tr>
</table></div>
<script>
var speed=30
marquePic2.innerHTML=marquePic1.innerHTML 
function Marquee(){ 
if(demo.scrollLeft>=marquePic1.scrollWidth){ 
demo.scrollLeft=0 
}else{ 
demo.scrollLeft++ 
} 
} 
var MyMar=setInterval(Marquee,speed) 
demo.onmouseover=function() {clearInterval(MyMar)} 
demo.onmouseout=function() {MyMar=setInterval(Marquee,speed)} 
</script>