This is totally unscientific, but I like to write experimental apps that manipulate the DOM heavily and Firefox is very often the fastest between Chrome and Safari in repainting the DOM (this wasn’t the case ~3 years ago).
There is a lot of cruft in Chrome's engine that accumulated over the years. Meanwhile, Firefox had a lot of the engine logic rewritten from scratch, using Rust.
This is less of an issue of Chrome being slow and more about measuring different things across the two browsers because of how the micro benchmark is structured.
This is totally unscientific, but I like to write experimental apps that manipulate the DOM heavily and Firefox is very often the fastest between Chrome and Safari in repainting the DOM (this wasn’t the case ~3 years ago).