This is a (Firefox) add-on (WebExtension) that lets you invert the website's color scheme by inverting/changing the prefers-color-scheme
media feature of CSS without requiring you to change the whole system style setting.
Test websites:
This extension only works with modern Firefox v95 or higher. Versions before v1.0 do support older browser versions, but use a more error-prone way of darkening websites.
You can easily get involved in this FLOSS project and any help is certainly appreciated. Here are some ideas:
Or, in any case, support us by spreading the word! ❤️
If you want to find out how this add-on currently works on a technical level, have a look at this Stackoverflow answer. I've explained it there in detail.