javascript global variable doesn't set in javascript

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Javascript

I'm very new to javascript. I have a trouble in changing the value of javascript global variable. Here is my code.

In header.php file I have declared the global variable.

<script type="text/javascript">
        var name;

</script>

Then in index.php file I change the value of the "name" variable.

if (xmlhttp.readyState==4 && xmlhttp.status==200)
                                             {
                                                if(xmlhttp.responseText != null)
                                                    {
                                                 JSONObjList=xmlhttp.responseText;
                                                    if(JSONObjList!=null){
                                                         var JSONListObj = JSON.parse(JSONObjList);
                                                          if(JSONListObj.loggedIn == true){
//
                                                               name=JSONListObj.username+"|true";
                                                               alert(name);
                                                          }
                                                          else{
                                                              name="";
//                                                              logstatus="false";
                                                          }


                                                    }


                                                 window.location = "http://localhost/mvc/myplaylist";
                                                    }
                                                    else{
                                                  document.getElementById("myDiv").innerHTML="Login details are incorrect";
                                                  form.email.value="";
                                                  form.password.value="";
                                             }

Here alert(name) gives the required value. Then I want to access that value again in header.php as in the following.

<script type="text/javascript">
                                             alert(name);
                               var arr=name.split("|");
                               if(arr != null)
                                   {

                                       var status=arr[1];
                                       var inputstr=arr[0];
                                   }
                               if(status =="true"){

                                       document.write("<td id='log' rowspan='2'onMouseOut='MM_swapImgRestore()' onMouseOver='MM_swapImage('Image4','','images/bttnn/btn_logout.png',1)' onclick='DestroySes()'><img src='images/bttnn/btn_logout_h.png' alt='Log Out' name='Image4' width='150' height='56' border='0'</td>");
                               }
                                else
                                      document.write("<td id='log' rowspan='2'><a href='#login_form' id='login_pop'onMouseOut='MM_swapImgRestore()' onMouseOver='MM_swapImage('Image4','','images/bttnn/btn_login.png',1)'><img src='images/bttnn/btn_login_h.png' alt='Log In' name='Image4' width='150' height='56' border='0'></a></td>");

                          </script>

Above code works fine for Chrome. But when I run it in Firefox name value prints nothing in header.php

Can anybody explain me the reason.