https://jlelse.blog/micro/2022/12/2022-12-13-nsdzc
A comment by shscs911:
Changing the pref, `browser.download.start_downloads_in_tmp_dir` in `about:config` to `true` fixes it for me.
https://connect.mozilla.org/t5/discussions/firefox-now-saves-files-that-i-only-wanted-to-open/m-p/12878/highlight/true#M5764