Here is my HTML file (jQuery needed and enable HTML5 in FireFox about:config)
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" src="js/jquery/jquery-1.4.2.min.js"></script>
<script type="text/javascript">
$(document).ready(function() {
$('svg').append("<rect x='100px' y='0px' height='100px' width='100px' fill='red' />");
})
</script>
</head>
<body>
<svg viewbox="0 0 300px 600px">
<rect x='0px' y='0px' height='100px' width='100px' fill='blue' />
</svg>
</body>
</html>
The problem is that I can't see red rectangle when I load this page. In firebug, the red rectangle square is like this darkened.