So, turns out my previous comment, which I have now deleted, was due to a false positive while troubleshooting Firefox to find what caused an ungodly high memory usage (>95% of RAM eaten). There are still some problems with Dark Reader, it won't remember the settings for some websites or won't turn itself on or off on some pages for some unknown reasons, but, overall, it does it's job in a good way.

Excellente extension !

Great add-on, very useful for using my computer at night. The only thing is that I can't seem to turn it off? I can adjust the settings and switch between Dark/Light modes, but when I try to use the "Off" button or the keyboard shortcut nothing happens. Several times, when I've been using my computer in the day and didn't want an extremely dark or desaturated screen on webpages, I've just uninstalled the extension and reinstalled it later. This is obviously very annoying, though.

EN:
The best extension of its kind. Everything stated is there. Safe, open source and mozzila tested, updated regularly.

RU:
Лучшее расширение в своем роде. Всё заявленое есть. Безопасно, открыт исходный код и проверен mozzila, регулярно обновляется.

A great extension for the eye