In Firefox 70 we changed how pixels get to the screen on macOS. This allows us to do less work per frame when only small parts of the screen change. As a result, Firefox 70 drastically reduces the power usage during browsing.

While reading this, I found a bunch of parallels between Firefox and Acorn with regards to compositing. Acorn draws to an IOSurface like Firefox, but I've got some interesting code for doing partial updates to big Metal textures, so Acorn does as little copying as possible.