onReadyStateChange Firing in Safari and Opera but not in Firefox

JavaScript
1

I have a simple XHR request that works well in Safari and Opera but not in Firefox. I have the following code:

function AJAX(ajaxurl, ajaxdata, ajaxcallback){
	if(!ajaxcallback) ajaxcallback=function(){};
	
	var ajaxreqobj = new XMLHttpRequest();
	
	var ajaxpostdata = "";
	for(var ajaxi in ajaxdata){
		ajaxpostdata += "&"+ajaxi+"="+encodeURIComponent(ajaxdata[ajaxi]);
	}
	
	ajaxreqobj.open("POST", ajaxurl, false);
	
	ajaxreqobj.callback = ajaxcallback;
	ajaxreqobj.onreadystatechange = function(){
		if(this.readyState==4 && this.status==200){
			this.callback(this.responseText);
		}
	}
	
	ajaxpostdata = ajaxpostdata.substr(1);
	ajaxreqobj.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
	if(navigator.userAgent.indexOf("Firefox/3")!=-1){
		ajaxreqobj.sendAsBinary(ajaxpostdata);
	}else{
		ajaxreqobj.send(ajaxpostdata);
	}
	
	return ajaxreqobj;
}

var ajaxdata = new Array();
ajaxdata["stage"] = "init";
var ajaxobj = AJAX("ajax.php", ajaxdata, function(){alert("Hello");});

Firebug indicates that “ajax.php” succesfully loaded; in fact, the value of “ajaxobj.readyState” is 4 and “ajaxobj.status” is 200! However, in Safari and Opera, I receive the “Hello” alert box, but in Firefox, I don’t. In fact, no code at all is running inside the “onreadystatechange” event; I know this because I set a breakpoint.

Making Firefox 3 use the standard “ajaxreqobj.send(ajaxpostdata);” does not fix the problem.

What in the world is making my simple AJAX request work in Safari and Opera but not in Firefox?

2

Okay, I found my problem. I had been sending my request synchronously instead of asynchronously by accident. Apparently Firefox doesn’t fire the readystatechange event on synchronous events. But this error helped me find a more important error in my code (: