ช่วยด้วยครับ ติดปัญหาเกี่ยวกับ ajax คือว่า HttPRequest.responseText ใน IE มีค่าตรงกับทีส่งมาครับ แต่ใน Firefox ,Chrome ไม่มีค่าครับ

function login() { 
       var HttPRequest = false; 
			if (window.XMLHttpRequest ) { // Mozilla, Safari,... 
		var	HttPRequest = new XMLHttpRequest(); 
		
			
			     if (HttPRequest.overrideMimeType) { 
				     HttPRequest.overrideMimeType('text/html'); 
				} 
				
				
          } else if (window.ActiveXObject) { // IE 
					try { 
							HttPRequest = new ActiveXObject("Msxml2.XMLHTTP"); 
						} catch (e) { 
							try { 
									HttPRequest = new ActiveXObject("Microsoft.XMLHTTP"); 
							} catch (e) {} 
					}						 
				}  
				if (!HttPRequest) {     
				alert('Cannot create XMLHTTP instance');         
				return false;         
				}

var usr = document.getElementById('usr').value;
var psw = document.getElementById('psw').value;
var type = document.getElementById('type').options.value;

var url = 'login.php'; 
var pmeters = 'usr='+usr+'&psw='+psw+'&type='+type;

//alert(pmeters);

HttPRequest.open('POST',url,true);            
HttPRequest.setRequestHeader("Content-type", "application/x-www-form-urlencoded");        
HttPRequest.setRequestHeader("Content-length", pmeters.length);       
HttPRequest.setRequestHeader("Connection", "close"); 
HttPRequest.send(pmeters);  
HttPRequest.onreadystatechange = function()          
		{         
	
		if(HttPRequest.readyState == 4) // Return Request                  
				{   
				
					alert(HttPRequest.responseText);
					if(HttPRequest.responseText=="admin"){
						
						window.location="admin.php";
					}else if(HttPRequest.responseText=="manager"){
					    window.location="welcome.php";   
					}else if(HttPRequest.responseText=="depleader"){
					   window.location="welcome.php"; 
					}else if(HttPRequest.responseText=="grpleader"){
					   window.location="welcome.php"; 
					}else if(HttPRequest.responseText=="user"){
					   window.location="welcome.php"; 
					}else if(HttPRequest.responseText=="0"){
					    document.getElementById('psw').value='';
						alert('Username or Password incorrect.');
					}else if(HttPRequest.responseText=="2"){
					   
                        document.getElementById('psw').value='';
						alert('Your account has been disable.');
					}else{
					    document.getElementById('psw').value='';
						alert('Access denied for your account');
					}
				} 
		} 
}