I have tried a few dark modes for firefox and so far this is my best experience. No youtube invert, not making websites that already are dark any weird/buggy, and lets you have parameters.

Some sites have contrast problems, but for the majority of sites, it works really well! Must have extension for sure!

It just doesn't work on some sites like the addons.mozilla.org one

Great add-on for dark mode with many customable settings. It works nearly everywhere. However the best looking mode "dynamic" is quite performance intensive and it does not work everywhere; e.g. Azure DevOps, the left menu and the top part stays unchanged.

Works best compared to the other dark theme extensions!

Best dark extension for Firefox !