在windows.onload()中，IE可正常设置marginTop，而火狐(margin-Top)却不能

Question

下面是代码        window.onload = function() {
            var varWinHeight = window.screen.height;
            var varMain = document.getElementById("main");
            var varMainTop = varWinHeight / 2 - 130;
            if (window.ActiveXObject)
                varMain.style.marginTop = varMainTop;
            else 
                varMain.style["margin-top"] = varMainTop;
        }在IE中会起作用，而火狐中却不起任何作用。这是什么问题？

Answer 1

varMain.style.marginTop = varMainTop + "px";

Answer 2

varMain.style.marginTop = varMainTop + 'px';FF也是这样拿marginTop的值

Answer 3

lz   不用判断             直接写这个就行 
       varMain.style.marginTop = varMainTop;
            

Answer 4

      window.onload = function() {
            var varWinHeight = window.screen.height;
            var varMain = document.getElementById("main");
            var varMainTop = varWinHeight / 2 - 130;
            varMain.style.marginTop = varMainTop;
         }