I would call it usable, but not "very usable". For normal people, Chrome(ium) UX is better. For power users, Vivaldi is a far better choice despite the Chromium browser engine. And for both of these groups, Firefox UX worsens and improves seemingly at random.

Quite frankly, I'm conflicted whether I should recommend Firefox at all. If I say "look, here's Firefox! It's more private than Chrome, and almost as fast and error-free!", and then Mozilla goes on to ruin that perception 6 months later (as they are wont to do), then it's my reputation and credibility at stake. Not only is that an unnecessary ego hit, but also makes me look like a liar (or at best, like an ivory tower dweller divorced from reality).