The CSS engine was completely rewritten in Rust and now heavily utilizes parallelism, which Rust certainly did help with. I'd say, this was only about 1/4 of the performance increase going from 56 to 57, though. (Based on my perception, having run Nightly as daily driver and being aware of when which bigger change got merged.)<p>The rest of the performance work was untied from Rust, as far as I'm aware.<p>Upcoming somewhen after 57 is also WebRender / Quantum Render, which should give a significant boost to FPS. Basically, if you've ever wondered why your gaming PC can render out giant space warfares at 120 FPS, but your browser starts stuttering when that super cool menu animates itself, WebRender is going to fix that in principle.<p>So, there's still going to be other problems, like JavaScript performance just not being on par with compiled code, but it should bring us a lot closer to the FPS that you'd expect.<p>(To throw in some technical terms, in case you want to research: Browsers so far used Immediate Mode to draw things, whereas WebRender and video games use Retained Mode.)<p>And WebRender was architectured as part of Servo, so is also written in Rust, but I can't tell you, if Rust really benefitted work here, or if it just happens to be written in Rust.<p>This illustrates the sort of difference we're looking at with WebRender: <a href="https://www.youtube.com/watch?v=u0hYIRQRiws" rel="nofollow">https://www.youtube.com/watch?v=u0hYIRQRiws</a><p>(Mind, though, that the video is more than a year old now. Firefox 57 should also already perform a lot better than what is shown in the video. Then again, WebRender is VSync-capped in the video...)