I would say, it kills my iOS, my MacBook and my Linux. It's shit.
I thought my iPhone 13 was broken, but it turns out, if I never start Firefox, it works perfectly.
A couple of years ago I think they had some performance problems with a lot of tabs. Seems like they're back to having the same problems they used to have. I've worked at places that kept re-introducing the same software bugs month after month. Certain way to lose your customers.