js两侧图片代码为什么不兼容ff 在ie中正常显示

我是新手 js两侧图片代码为什么不兼容ff 在ie中正常显示，在ff中图片跑到网站下面了并且网页左下面只显示一张 请高手解决

js代码如下：
function initEcAd() {
document.all.AdLayer1.style.posTop = -200;
document.all.AdLayer1.style.visibility = 'visible'
document.all.AdLayer2.style.posTop = -200;
document.all.AdLayer2.style.visibility = 'visible'
MoveLeftLayer('AdLayer1');
MoveRightLayer('AdLayer2');
}
function MoveLeftLayer(layerName) {
var x = 5;
var y = 150;// 左侧广告距离页首高度
var diff = (document.documentElement.scrollTop + y - document.all.AdLayer1.style.posTop)*.40;
var y = document.documentElement.scrollTop + y - diff;
eval("document.all." + layerName + ".style.posTop = parseInt(y)");
eval("document.all." + layerName + ".style.posLeft = x");
setTimeout("MoveLeftLayer('AdLayer1');", 20);
}
function MoveRightLayer(layerName) {
var x = 5;
var y = 100;// 右侧广告距离页首高度
var diff = (document.documentElement.scrollTop + y - document.all.AdLayer2.style.posTop)*.40;
var y = document.documentElement.scrollTop + y - diff;
eval("document.all." + layerName + ".style.posTop = y");
eval("document.all." + layerName + ".style.posRight = x");
setTimeout("MoveRightLayer('AdLayer2');", 20);
}

document.write("

"+"");
initEcAd()

// JavaScript Document