when I click on a PDF on a website, Firefox does what is specified under Settings/Applications for "Portable Document Format (PDF) (application/pdf)". I prefer to open the PDF in the Adobe Acrobat Reader, but apparently, the browser prefers to save PDF files. When I save my preferences "open with Adobe Acrobat Reader", it does that, but the next day, it tries to save the PDF again. This has been so for a long time. An overlooked bug or a feature?