Javascript在mozilla firefox中不起作用

以下代码在mozilla firefox中不起作用镀铬效果良好使用的操作系统是linux在代码中，我一直在更改任务栏的顶条颜色和内容，在滚动后还有一个浮动的联系人按钮在左侧，需要在传递某些div元素后显示。提前感谢

window.onscroll = function (oEvent) { //onscrool
var mydivpos = document.getElementById("aboutus").offsetTop;
var mydivpos2 = document.getElementById("mainlogo2").offsetTop;
var mydivpos3 = document.getElementById("home").offsetTop;
var scrollPos = document.getElementsByTagName("body")[0].scrollTop;
if(scrollPos >= mydivpos)
{
    document.getElementById("noshow").className = "";  //changin the classname
 }
else {
 document.getElementById("noshow").className = "hidden"; //the topbar which is need to show
}
if(scrollPos >= mydivpos2)
{
   document.getElementById("topbarwithlogo").className ="";
    document.getElementById("topbar").className = "hidden";
 }
if(scrollPos == 0)
{
   document.getElementById("topbar").className ="";
    document.getElementById("topbarwithlogo").className = "hidden";
 }
};


//HTML
<div id="noshow" class="hidden">
    <div class="appiphycontact">
                        <ul>      
                                    <img src="logos/facebook.png"   class="img-responsive">
                                            <img src="logos/google+.png" class="img-responsive">
                                            <img src="logos/Linkedin.png" class="img-responsive">
                                            <img src="logos/twitter.png" class="img-responsive"> 
                                    </ul>   
    </div> 

<div class="container-fluid" id="topbar">
        <nav class="navbar" role="navigation">
            <div class="navbar-header">
                <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#bs-example-navbar-collapse">
                     <span class="sr-only">Toggle navigation</span><span    class="icon-bar"></span><span class="icon-ar"></span><span class="icon-bar"></span>
                </button>       
            </div>
                <div class="collapse navbar-collapse" id="bs-example-navbar-collapse">
                  <ul class="nav navbar-nav" id="ul">
                    <li>
                        About Us
                    </li>
                    <li>
                        Our Team
                    </li>
                    <li>
                    Our Clients
                    </li>                       
                </ul>
            </div>
    </nav>

 <div class="container-fluid hidden" id="topbarwithlogo">
        <nav class="navbar" role="navigation">
            <div class="navbar-header">
                <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1">
                     <span class="sr-only">Toggle navigation</span><span class="icon-bar"></span><span class="icon-bar"></span><span class="icon-bar"></span>
                </button> 
                      <a class="navbar-brand" href="#"></a>
            </div>
                <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
                <ul class="nav navbar-nav navbar-right" id="ul">
                    <li>
                        About Us
                    </li>
                    <li>
                        Our Team
                    </li>
                    <li id="li">
                    Our Clients
                    </li>                       
                </ul>
            </div>
    </nav>
</div>
  <div class="container-fluid" id="home">
  <div class="tinted-image">    
      <div class="container">
            <div class="col-md-12" id="mainlogo2">
                                <img src="images/someimage.png" class="img-responsive" alt="">
            </div>
    </div>
                <div class="container-fluid">   
                    <div class="maincontent">
                            <div id="maincontent"><h1>.</h1> 
                                </div>
                 </div>
                </div>                   
     </div>

<div class="container-fluid aboutus" id="aboutus">
            <div class="container">
                    <h2>About Us</h2>
                    <p class="aboutusheader2">LEADER IN IT SERVICES, DIGITAL AND BUSINESS SOLUTIONS</p>
                    <div class="row">
                            <div class="col-md-6 imagediv ">
                                <p id="aboutusinfo" >Some information.</p>          
                            </div>

                        <div class="col-md-6 imagediv">
                                    <div class="aboutusimg">
                                                    <ul>
                                                                <img src="images/someimage.png" class="img-responsive" alt="">
                                                    <img src="images/someimage.png" class="img-responsive " alt="">
                                                            <img src="images/someimage.png" class="img-responsive" alt="">
                                            </ul>
                                    </div>
                          </div>
  </div>
 </div>