In Firefox Settings I have PDF downloads set to 'Always Ask' ... this used to work well enough (although, depending on my file download dialog choice to 'Open with Firefox', 'Open with - Adobe Acrobat Reader DC' or 'Save File', I seem to be accumulating duplicate PDF file copies in Downloads\Mozilla.org\Downloads ... the duplicate file redundancy is very annoying), however, with the latest update to Firefox, now I am unable to direct download PDFs from the down-arrow symbol within a given e-mail's Gmail attachment icon ... I can view the file in Gmail by clicking on the body of the Gmail attachment icon but the download button within the Gmail file viewer (top right) doesn't work either. So far as I can tell, this behaviour is confined to Gmail alone (i.e.: https://mail.google.com/mail/u/1/#inbox) ... I am able to get the file download dialog for PDF document download links at other websites and successfully retrieve PDF files. What have the developers changed now? Whatever it was, quit it.