Downloading is possible for both photos and videos from posts, as well as for stories, reels or profile picture.
This issue that probably fixed in latest version
I'm on v2.2.17 as the time of this writing. I believe it supposed to work; perhaps it's something on my Firefox. No big problem, I'm still able to fully use it on Chrome. Thanks! :)
Does not work (no download button) on Greasemonkey v4.11 (Firefox), works correctly on Tampermonkey v4.15 (Chrome).