Okay I have found this theme that makes Firefox look more like Safari, which is not too bad I guess?

https://github.com/AdamXweb/WhiteSurFirefoxThemeMacOS

https://cdn.nostrcheck.me/74c5a7e59cf60cfdd2d375f4ceb25f67dea76bf001c2720598988733d59ae69d/402e2635330b87d497518d5a3138d379a41c371a564594aae2e6480a379d7712.webp