JS code working on IE10 but not on mozilla, chrome ...

function show_packet(str, company)
{
var cam=document.getElementById("company");
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  var xmlhttp=new XMLHttpRequest();

  }
else
  {// code for IE6, IE5
  var xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }

    xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {

    document.getElementById("packet_1").innerHTML=xmlhttp.responseText;
    document.getElementById("icon_1").innerHTML="";
    }
  }

xmlhttp.open("GET","show_packet.php?car_moto="+encodeURIComponent(str,true)+"&cam="+encodeURIComponent(cam.value,true));
xmlhttp.send();

}