I wouldn't say it's only speed. I've been Firefox for years, but eventually ended up surrendering Apple eco-system. with Apple silicon, Firefox at least then wasn't sleeping that well, and the tab sync of FF between my devices was also less than I've desired.

So performance is general is more like it... that includes not hurting my battery life.

I've used all 3 browsers (chrome/safari/ff) daily doing web dev for years now and I'm convinced Safari just feels faster as a cohesive Mac app, with the animations and what not, but isn't in general when using the internet day-to-day. FF is little different than Chrome/Safari.

Also as a dev Safari is becoming the new IE. I've had a whole suite of Safari-only bugs in the past 2yrs and lots of browser crash reports from users.