Built-in dark mode for web contents

[batata]

I love extensions like Dark Reader that automatically transform any website with a dark theme. The way they do this is by injecting many new styles into the DOM, it works but there is two main drawbacks to this method :
- there's a latency that makes contents blink
- it reduces performances on some websites by a lot

So It would be great if there could be a built-in low level solution (directly in web render?) that would swap colors on the fly without editing the page styles and thus would solve the two aforementioned issues.

[sus_scrofa]

I would also love to see the idea finally implemented. In the meantime, I'm using Ultima Dark, an open-source addon that is agressively enough and avoids white flickering: https://addons.mozilla.org/en-US/firefox/addon/ultimadark/

(I'm not affiliated in any way with the development of the addon, just a user of it.)

It would be a dream to have this feature implemented di into firefox, since the source code already exists, so I could not just decide if I want a website to use enhanced tracking protection, my webcam, microphone etc. but also if I want a website to be darkened or not (e.g. because it already has a great dark mode)