Works great!

Improvement Idea:
It would be nice to have a "Quick Switch" option to directly toggle dark mode on/off when left clicking the addon's tooltbar icon. Could then add Quick Switch on/off to the toolbar icon's right click context menu to get back to the normal settings.

Slows down browsing big time. Not recommended.

I like this one better because it's simple to adjust (vs the other one). HOWEVER, FF now says it's unsigned and can't use it!!! Developer, please update your app so I can download it to use again.