I've had some experiences like that, mostly when Spectre/Meltdown were new. (or if I had a dGPU which didn't have good drivers - or.. if there's no hardware acceleration for smooth scroll for some other reason, like chrome on ARM for a long time).

I agree that it's a dealbreaker, and the circumstances in which it can happen are opaque and difficult to troubleshoot.

Luckily these days with anything released since 2020- it's a lot better. Linux still struggles a lot with JS runtimes on Skylake.

While I am throwing Linux under the bus a bit here, I am still perplexed that we use an exceptionally inefficient language as the major application delivery system of the modern day. We complain that it uses a lot of RAM and is slow, but if you consider what javascript is compared to how CPUs think about things, it's a miracle we get what we get... we managed to get a marvel of engineering and the response has been to shove millions of lines of code through it... At some point, yeah, it's slow.