Yes, if you have your PDF handling set to "Open in Firefox" then Firefox will try to always open PDFs even if the server tries to discourage it. In some cases, the PDF will open as web content (URL starts with http: or https:) and in other cases, the PDF will open after saving to disk (URL starts with file:).
Could you describe how you want it to work? For example:
(1) Always ask whether to open or save
(2) Always open as web content rather than saving to a local folder
(3) Something else
