Sending FormData with file fields shuld result in content-type "multipart/form-data". JQuery set it to "application/x-www-form-urlencoded" which is wrong.

content-type header should be left alone in such cases so xhr object will set it to a proper "multipart/form-data" + proper boundary, by him self.

FormData is experimental stuff so I dont care if it is not supported. The real problem here is ther is no way to say to jquery to not set content-type header.

I am refering to this :

if ( s.data || origSettings && origSettings.contentType ) {
  xhr.setRequestHeader("Content-Type", s.contentType);
}

As long as there is some data to send jquery will set something in Content-Type, this is good, but there should be a way to override this...

When I am talking about FormData I refere to this :

FormData