I have been using it for years, on desktop and mobile devices both. It's the best of its kind for Amoled displays. Overall, I am very satisfied with it.

Naturally, it's not working as smoothly as it used to with v.57. Aside from the known and unfixable issues mentioned already by the developer, I'd like to point out that it takes a while to "black out" almost all websites that I visit. It's not nearly as instantaneous as before, the performance feels more than a little laggy. Keep in mind that I'm referring exclusively to the Android version of FF..