Firefox 45 has introduced a regression where submitting a
<form enctype="multipart/form-data"> with an empty
<input type="file"> fails to send the
Content-Type HTTP header as well as the
filename field in the
Content-Disposition header, potentially breaking the application’s server-side logic while parsing the form data.
Content-Disposition: form-data; name="multipartFileList"
Content-Type: application/octet-stream Content-Disposition: form-data; name="multipartFileList"; filename=""
This bug has been fixed with Firefox 45.0.2.