Firefox has taken a cue from Chrome and now offering the “Open in System Viewer” and ” Always Open in System Viewer” options for downloaded PDFs in its Download Panel.
Google Chrome, Microsoft Edge (both legacy and new), and Firefox browsers have PDF Viewer built-in. Recently these browser vendors started working on improving and adding new features to their PDF Viewers.

Google Chrome by default instead of opening PDFs in the browser, downloads them. The downloaded PDFs appear at the bottom.
For a PDF file you saved, Chrome offers open, Open with System Viewer and Always Open with System Viewer options. Here System Viewer means, Default PDF Application on Windows.

We don’t need to tell you new Microsoft Edge is the default PDF Reader on Windows 10, so here, System Viewer means Edge unless you change it to any other PDF application.
Following the recent PDF Viewer improvements, Mozilla has added two new options to downloaded PDF’s context menu in Downloads panel, like Chrome, they’re:
- Open in System Viewer
- Always Open in System Viewer.
Selecting the former, opens the PDF in Edge in App mode once for that PDF, whereas when you select the latter, whenever you click on PDF, it will always open in the default PDF Reader.
Since the downloads icon in Firefox doesn’t always visible, to access or see these options anytime, click on Library icon > Downloads and right-click on PDF file.
Related articles:
Google Chrome: How to Always Open PDFs with System Viewer?
New Microsoft Edge to open PDFs in App Mode in Firefox
Firefox can now be set as default PDF Reader in Windows 10
PDF.js to get Huge Memory Improvements in Firefox 33