My website has been running for many months, and as part of the site users can upload PDF documents to share with others. The last successful upload was 5th Nov, but to-day my upload was rejected because Firefox returned the document type as application/force-download rather than application/pdf. Uploads work fine with IE8. The site uses PHP to check extension and document type and, as I mentioned, has worked fine for many months. I have even attempted to upload the same document that succeeded on the 5th, but again Firefox returns application/force-download as the document type. Why the change?