<!DOCTYPE html>
<html>
<body>
<h1>My First Web Page</h1>
<p>My first paragraph.</p>
<p>
Activate debugging in your browser (Chrome, IE, Firefox) with F12, and select “Console” in the debugger menu.
</p>
<script>
console.log(5 + 6);
</script>
</body>
</html>
If this is to be work well in Firefox,,then Firebug need to be open ,ot it would result in page crash!