Upload Tab Not Appearing After Following Instructions

Hello, I'm having some trouble getting the upload tab to appear in the image pop-up window. It currently shows three tabs, Image Info, Link, and Advanced. I followed the instructions and added an uploader script called upload.php. Here is the code to create an instance of the editor:

<script type="text/javascript">
   window.onload = function() { CKEDITOR.replace( 'editor1', { uiColor : '#9AB8F3', filebrowserUploadUrl : '/upload.php', filebrowserImageUploadUrl : '/upload.php' } ); };
</script>

The above code is not working. Can someone give me a quick pointer on what I might be doing wrong? Any help would be appreciated. Thanks!