Starting with Firefox 56.0.2, ASP Uploader no longer functions properly.  The form shows up, and you can select a file but as soon as you start the upload, the browser logs an error Oxa2 is null.   I have repeated this on 4 seperate computers, and I can verify that it happens on your test page at http://aspuploader.com/demo/form-multiplefiles.asp as well.

Any ideas?