I found an old screenshot from the extension page. Last year it had 7000 users and 9 reviews. Compared to uBlock Origin (6 million users, 15k reviews) and AdBlock for Firefox (1 million users, 3k reviews) I'd say it was not an official add-on and trying to cash in on SEO. URL was /get-adblocker-free, title 'AdBlock Free', author 'Adblock' (apparently different author than 'AdBlock' or names are not unique).

>AdBlock was sold to an anonymous buyer in 2015

And immediately started allowing "acceptable ads", selling usage data & AdBlock Plus came to be. I thought the original was dead already. Mozilla should have blocked it 7 years ago.