I see GP's point tho. The original Greacemonkey was open-sourced. Tampermonkey was the successor and is proprietary. Violentmonkey came to fix that. I wouldn't be surprised if Mozilla rejected TM because of not being OS and rejected VM because of lack of popularity
I get what you mean, and it'd be cool if "Recommended" was only for FOSS, but I don't think that ever been the case? Probably lots of the "Recommended" extensions are proprietary, from https://addons.mozilla.org/en-US/firefox/search/?promoted=re... you don't get far before hitting one, the 3rd extension already is proprietary out of those, surely more.
> Violentmonkey - Rating 4.7 (793 reviews) - 164,622 Users
On Google Web Store, it's 11,000,000 users VS 900,000 users.
Their popularity seems different by a magnitude, hardly surprising Firefox/Mozilla would chose to focus on one above the other.