I am revising code that uses XMLHttpRequest for a file upload. I have just learned that this is a v2 feature and unavailable in IE9. If I swap the ajax call out to jQuery, as discussed in the question, How to send FormData objects with Ajax-requests in jQuery?, do I have any hope of this working from IE9?
I am using this library at work for fileupload via ajax: https://github.com/blueimp/jquery-file-upload. It is working nicely with IE 9, it can even support CORS if you use a redirect frame.
It also support the formData you are talking about i think:
https://github.com/blueimp/jQuery-File-Upload/wiki/Options#formdata