I was already using 55.x Beta. My BIGGEST issue, is that EVERY browser seems to chew up memory over time, just by leaving it open with tabs going. Firefox, Chrome, Safari. All do the same thing. Alleviated by using the Great Suspender in Chrome, but why can't they all have this just built in? Startup/speed, and initially memory use really haven't been that big of an issue. It's the memory, and finally grinding to a halt that is the BIGGEST issue for me. I can't escape it.

Happens on MacOS, and Windows for me.