There are also some other ways to fix cufon for IE9 if you are unable (or unwilling) to replace the js file.
<!--[if gte IE 9]>
<script type="text/javascript">
Cufon.set('engine', 'canvas');
</script>
<![endif]-->
Alternatively, you can always force ie9 to render as ie8 or ie7:
<meta http-equiv="X-UA-Compatible" content="IE=8" />
<meta http-equiv="X-UA-Compatible" content="IE=7" />