Use system viewer for downloaded PDFs, use Firefox's built-in viewer for all others

Firefox version: 78.0.1

Firefox recently changed the behaviour when clicking on downloaded PDFs in the Firefox Downloads panel. While all other downloaded files are opened with the system default program when clicking on them, PDFs are opened with the built-in Firefox viewer.

This is counter intuitive. If Firefox is the system default PDF viewer, this separate treatment of PDFs is not necessary (the system default redirects back to Firefox). If Firefox is not the system default PDF viewer, users need to take extra steps to open a PDF in the system viewer after downloading (open the folder, click on the file; also documented here: It looks like this change creates no benefit for those who use Firefox as the system default PDF viewer, while reducing usability for those who use a different system PDF viewer (e.g., Acrobat).

Example use case:

  • Browse to a PDF URL: use the Firefox built-in viewer, because it is fast and convenient. A more sophisticated viewer is not necessary because the document is only viewed, not edited.
  • Download a PDF: use the system default viewer (e.g., Acrobat), for example for annotation.

Is there an option to disable the Firefox built-in viewer for downloads, while using it for URLs?

The approach in beta requires using the right-click context menu to launch a PDF from the Downloads list in an external viewer:


There’s also a menu item to change the global handling of PDFs. What there isn’t, it seems, is a preference to toggle between using Firefox or using the system view when launching PDFs from the Downloads menu. That would be more convenient.