Dark Mode Website Switcher 
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:
- https://stuffandnonsense.co.uk/blog/redesigning-your-product-and-website-for-dark-mode
- https://webkit.org/
- https://pinafore.social/
- https://s.codepen.io/aardrian/debug/NmoQdN
- http://adrianroselli.com/
- https://emojipedia.org/
- https://bugzilla.mozilla.org/
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.
Download
Contribute
You can easily get involved in this FLOSS project and any help is certainly appreciated. Here are some ideas:
- 📃 Translate this add-on into multiple languages!
- 🐛 Fix some easy issues and get started in add-on development (or just try out the development version)
- 💡 Or check out some other add-on issues (or translate them).
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.