javascript style.display =

写了一个控制div显隐的js,代码如下：
<script language = javascript >
           function changemethod(mode){
           if(mode == "Coexp"){
              copnet1.style.display = "";
                 copnet2.style.display = "";
            diftab.style.display = "none";

            }else{
               copnet1.style.display = "none";
                  copnet2.style.display = "none";
             diftab.style.display = "";
             
             }
         }
 script>

在ie 下运行正常，在firefox下失效，解决方法
删掉第一行