Hold down the control key while you click (two-finger click) the magnifying glass icon of the PDF file and select Show in Finder. To open a PDF file you downloaded in Firefox using another viewer: 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.
