Recently as in the last 8 years when they overhauled it. It really was slow as heck back in 2016, but the e10s effort really, really paid off in terms of performance.

It runs noticeably faster than chrome on my 12 year old laptop. Plus, it isn't riddled with invasive tracking garbage.

Even before then, 99% of the difference came down to whether chrome and firefox were properly using gpu acceleration. (Both could be easily misconfigured.)

I never saw a situation where the actual engine performance mattered in real world scenarios.

These days, all the engines are comparable, except that Google sabotages safari and firefox on its own sites.

It was definitely slower than Chrome with numerous tabs when I switched (again) some time in the last two years.