Me too and I don't really understand why. On Windows, pressing F12 to open Dev Tools takes a good five seconds in Edge but takes fractions of a second in Firefox. And page renders feel faster, although apparently they actually aren't in controlled experiments.
Maybe one of the extensions I typically use in both works differently in Firefox.
I'm on Linux, and Firefox's performance is still behind Chromium. Mozilla only recently enabled hardware acceleration. There are benchmarks in which Firefox beats Chrome (https://arewefastyet.com/linux64/benchmarks/overview?numDays... has an overview) but in general Chrome is faster.
On Windows and macOS Firefox is a bit more competitive, but important benchmarks such as JetStream and Speedometer still have Firefox easily beat (note the inverted score axes).
That doesn't mean Firefox is slow per se, it just means Chromium (and WebKit) are faster.
On Android I use Firefox for its addon support, but the UI is notably more glitchy and buggy than Chrome's.
These web apps are quite usable on Chrome and useless lag fests on Firefox.
Do I prefer the modern "let's ship a JS renderer with every webpage" approach? No, definitely not. Unfortunately, quite a few web applications and websites u visit disagree with me.
There's also a perceptable difference in terms of browser responsiveness outside the page itself. Firefox seems to take longer to process UI input in my experience, for reasons I don't entirely get. There's a slight but visible delay before the page starts rendering that Chrome doesn't have, and that small delay adds up when you're working in web UIs fir a significant part of the day.
Strange, on Linux I've found Firefox to be just as fast as Chrome. Granted, I've had all the hardware accel stuff force-enabled for years now, with no issues (on Intel iGPUs), so maybe that's why I haven't noticed any slowness.
This is the opposite of my experience on android. Firefox with uBlock Origin is the only way to get some sites to load in any reasonable timeframe. The difference can be measured in 10s of seconds, and is more noticeable with worse hardware.
Have you used it recently, or just years ago? It definitely used to be very slow, but since ~2 years ago it's very good, and my go to browser (my phone is not high end, by the way)