Firefox里无法实现DIV从右往左滚动？但是IE可以。该怎么处理

<script>
    var speed = 40
    democ2.innerHTML = democ1.innerHTML
    function Marquee1() {
        if (democ2.offsetWidth - democ.scrollLeft <= 0)
            democ.scrollLeft -= democ1.offsetWidth
        else
            democ.scrollLeft++
    }
    var MyMar1 = setInterval(Marquee1, speed)
    democ.onmouseover = function () { clearInterval(MyMar1) }
    democ.onmouseout = function () { MyMar1 = setInterval(Marquee1, speed) }
</script>