async attribute in script tag in Firefox
===

I'm trying to test the following code in Firefox 13.0.1, but it doesn't work correctly:

    <!DOCTYPE html>
    <html>
    	<head>
    		<title>Exercise 1</title>
    		<script type="text/javascript" async src="example1.js"></script>
    		<script type="text/javascript" async src="example4.js"></script>
    		<script type="text/javascript" src="example3.js"></script>
    	</head>
    	<body>
    		<p>Hello world</p>
    	</body>
    </html>

//example1.js:

    alert("I'm the example 1");

//example3.js

    alert("I'm the example 3");

//example4.js

    alert("I'm the example 4");

When I open the file which contains the above html code, the following occurs:

 1. In first place, a pop-up with the text "I'm the example 3" appears.
 2. In second place, a pop-up with the text "I'm the example 4" appears.
 3. In third place, a pop-up with the text "I'm the example 1" appears.

But the content inside the body tag doesn't display in the browser. The paragraph with the text "Hello World" should appear, but it doesn't.
The page load doesn't stop and the ring inside the tab in Firefox rotates continuously.

I don't know if my code is correct or is a bug from Firefox.

Thank you.

