This was driving me nuts: Even though I set #Firefox to always ask where it saves files, sometimes when I accessed PDF's it saved them in my Downloads directory without question.

It seems `browser.download.start_downloads_in_tmp_dir=true` solves this problem but I still can't wrap my head around why they implemented this exceptional behavior (and why there is no visible setting for it).

Source: https://www.reddit.com/r/firefox/comments/1jnpvs3/firefox_doesnt_ask_when_downloading_pdfs_and/