If you have your PDF preference set to Open in Firefox, then Firefox will save the file in the web content cache and treat it like embedded images and other cached content. If you have your PDF preference set to "Use Acrobat", then as mentioned in your other thread: Before Firefox 98, "Open with [application]" saved the file in the Windows TEMP folder, and passed that path to the application Starting in Firefox 98, "Open with [application]" saves the file in your default download folder, and passes that path to the application General article on download workflow changes: [[Changes to how file downloads are handled in Firefox version 98]]