


When Firefox is set as the default for viewing PDFs in the browser, you can still open downloaded PDF files with a third-party tool. Use a third-party PDF viewer for downloaded PDF files To learn more about the built-in PDF viewer, see Using Firefox's built-in PDF viewer (below). When you click on a link to a PDF file or open it from the Firefox Downloads panel, it will be rendered with the built-in pdf viewer. This built-in PDF viewer is enabled by default.

It can’t stop your web browser from opening online PDF documents.

This however only affects those local PDF files saved on your computer. Check out following steps to set Adobe Acrobat other than Edge as the default PDF viewer in Windows 10. If you have your own desktop PDF program on computer, such as Foxit, Adobe Reader, Adobe Acrobat, Sumatra, and would like to open PDF files using a classic PDF reader other than browser, you can set the PDF application as the default PDF reader on your computer. Almost all modern web browsers, such as Edge, Chrome, Firefox, come with built-in PDF reader so that users can view PDF files directly without leaving the browser.
