Hello. I have long had an issue with PDF downloading when just viewing even in anonymous view and being downloaded to Downloads and changing the date of the folder, which does not seem to behave anonymously. Anyway I used the about config and I am still using this method but that was not enough.
So I changed the default folder for downloads from Downloads to Desktop - now even when PDF downloads in anonymous view and deletes itself it does not change the date of change in my download folder.
Hope it can help somebody else too that has this issue with viewing PDFs and themselves downloading.
This is just a ramification of the initial unwelcomed, unexplained change of behaviour with pdf files downloaded even when just viewing them. After notorious userbase outcry, the original thread gets archived(denial or censorship? You choose) a "solution" is implemented as a setting when clearly it is required as default. I might be wrong, but I will never know, Mozilla doesnt seem to be interested in explaining WHY they changed to the new unwanted behaviour OR how it is not a matter of stubborn pride. I can't imagine better ways for alienating an already massively shrunk userbase.
In Firefox 103, the developers added a hidden option that enables using the web content cache to view more PDFs instead of saving to the "Save Files to" folder or the temp folder. This is only for people who set the PDF handling to "Open in Firefox". If you selected "Always Ask" then it doesn't work.
(A) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.
More info on about:config: Configuration Editor for Firefox. Please keep in mind that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.
(B) In the search box in the page, type or paste browser.download.open_pdf_attachments_inline and pause while the list is filtered
(C) Double-click the preference to switch the value from false to true (or click the toggle button toward the right end of the row)
If you are curious about the name of this preference:
A web server can send a Content-Disposition: attachment header to bypass viewing in a tab and force a download. This preference allows ignoring that for PDFs and treating them like other web content (AKA Content-Disposition: inline).