This is by far the best FF add-on I have, and it was just added a few hours ago. Nothing online is as important as being able to comfortably read and view images when browsing. If your eyes get hurt/strained it not only impacts your browsing experience but it can mess with your eye health long term. This add-on is allowing me to surf at night with minimal to no room lighting and not be blinded when a normally overly white page loads. I have just begun to play with the wide range of customizable options available. I am feeling a donation is heading to a dev after I play with this a little more and learn how to best use it.

This addons/extension is very good for my eyes because makes the websites dark so my eyes is not hurted anymore.

It works. And it often makes websites look better than the official dark theme. Easy to switch off on a per-website basis when something is obscured. The UI for that isn't obvious though (you have to click the website name in the Dark Reader box).