Hi Unajet, if you double-check the Options page, has Firefox saved the Open in Acrobat setting there? This article will get you to that setting: View PDF files using Firefox’s built-in viewer.

I've seen this question asked before but the solution given did not work for me. ... I've tried a couple of different solutions but nothing works.

What else did you try?

Do you notice this problem on a particular website, or does it happen with all PDFs from everywhere? Some websites do not send the PDF-specific Content-Type header (application/pdf) and then Firefox doesn't treat them like PDFs but instead like a generic kind of binary file. I created an add-on to work around that issue (when a file has a .pdf extension, it corrects the content-type):

https://addons.mozilla.org/firefox/addon/content-type-fixer/

I suggest keeping it turned off, and turning it on when you get to a site with that problem.

Yes, Adobe is already set up as the default .pdf program. I also found a solution where you delete a certain file that has your preferences so that you start over. It didn't work. All of the .pdf's that I'm trying to open are being sent over in Gmail using Firefox browser. They are invoices from different companies, but are all .pdf's.

Hmm, are they opening from the Gmail "attachments" domain, which I think is the usercontent one, or from Google Drive?

Either way, you could try my extension to see whether that resolves it.

Hi Unajet, In Options -> General page do you have Downloads set to Save files to...

And Applications set to Preview in Firefox

Yes, I have used both 'preview in firefox' and 'adobe' but not matter which one is listed, when I click 'download' on the actual file, it still wants to know every single time my choice.