While Firefox is waiting for you to choose a specific folder and customize the file name, it actually has already started downloading to the default download folder. But what is supposed to happen is that Firefox moves the download to your selected folder, not that it ends up in both folders. Possibly there is a permission problem preventing Firefox from deleting the initial file? As for when this started, maybe Firefox 98? Before that, Firefox for Windows used the system Temp folder for the background activity rather than the "Save files to" folder. You can switch back and see whether that avoids double-files. But this also will have the effect of using the Temp folder for any downloads you send directly to an external program rather than saving first (some users lost downloaded files that way, which was why it was changed). Here's how you change it if you want to give it a try: (1) 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]]. ''The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.'' (2) In the search box in the page, type or paste '''browser.download.start_downloads_in_tmp_dir''' and pause while the list is filtered (3) Double-click the preference to switch the value from false to true