How about https://github.com/mozilla/pdf.js/blob/master/src/shared/util.js#L1314 and use downloadUrl .

Otherwise we have to change https://github.com/mozilla/pdf.js/blob/master/web/firefoxcom.js#L75https://github.com/mozilla/pdf.js/blob/master/web/firefoxcom.js#L75 as well, and that's more testing for us.