This is one of the most vital and effective add-ons I've ever installed. Not every website/browser/etc has a consistent dark mode, and none handle it as well as Dark Reader. Needing to constantly research, this add-on saves my eyes at night. Even with recent changes to FireFox which temporarily hampered performance, Dark Reader quickly pushed an update and is straightforward about addressing issues. Honestly, this is probably one of the best add-ons next to an ad-blocker out there.