在IE中可以直接用obj.style.top=100;但在FireFox中必须加上单位，变成obj.style.top=100+'px';
style.left同理。
浏览器的判断：window.navigator.userAgent.indexOf("IE") == -1 //非IE浏览器 FireFox,Chrome
FireFox没有onmouseover和onmouseout,onclick事件,他们的写法为：
if(window.navigator.userAgent.indexOf("IE") == -1) //FireFox
{
link.addEventListener('mouseover', function(){a = false}, true);
link.addEventListener("mouseout",function(){a = true},true)
}
else //IE
{
link.attachEvent("onmouseover",function(){a = false});
link.attachEvent("onmouseout",function(){a = true});
}
{
link.addEventListener('mouseover', function(){a = false}, true);
link.addEventListener("mouseout",function(){a = true},true)
}
else //IE
{
link.attachEvent("onmouseover",function(){a = false});
link.attachEvent("onmouseout",function(){a = true});
}