If you have your PDF preference set to "Open in Firefox" -- see View PDF files using Firefox’s built-in viewer -- 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 there was a change:

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: How file downloads are handled in Firefox

I wish that was the answer. This just happened recently. It used to keep changing on it's own my setting to use Adobe and change back to save file. Now when I check, the settings have not changed on how to handle PDFs, but it still keeps saving when it's supposed to use Adobe. It's doing both opening and saving.

It's doing both opening and saving.

Files cannot be opened without being saved somewhere.

Before Firefox 98, "Use [application]" saved the file in the Windows TEMP folder, and passed that path to the application

Starting in Firefox 98, "Use [application]" saves the file in your default download folder, and passes that path to the application

Ok if I follow what you are saying then did Firefox 98 just come out in the last week or so as that is the only time this change has happened for me.

Yes, Firefox 98 was released last week.

Ok thank you for your help in clarifying. Bad name for the product release then as it is confusing. They just made it worse on those who liked how it worked before. And having no support for their product is terrible.