DITTO!
I just realized that my OS file system's "Downloads" folder is now bloated with files and docs that I ONLY viewed.
I have Firefox set to "ASK" what to do with every document so that I can choose to: View or download and WHERE to download to.
This new feature (a royal P.I.T.A is what it is) does automatically delete it's Firefox download log of files when closing the browser BUT leaves the "only viewed" file in my "Downloads" folder.
It is even so obnoxious that if I choose & click "download" and chose a specific folder (not downloads) and rename that file it will now save the file in two folders 1) in the folder I selected named as I named it and 2) under the files original name in my "Downloads" folder. How RUDE!
Firefox needs to fix this and I just had to verify, compare and delete over 200 DUPLICATE files.
At least add a user control setting.