I've been using this on Chrome for years! I recently switched to Firefox, and I was like, oh, I'm already learned not to waste my time on Facebook. Well, let's just say very quickly I learned how to dumb-scroll again. And it is mostly ads, I've been consuming SO many ads. Already bought a new shampoo. I am so glad this plug in works in Firefox too. In Chrome it even works on youtube, which became my biggest time sink.
EDIT: After installing, I saw it blocks Youtube in Firefox too~ awesome! biggest life upgrade