Opera GX allows you to limit the amount of CPU and RAM the browser can use. Much of this is of course marketing, properly implementing this can be hard, but it would have been interesting to compare how well this works.

https://www.opera.com/gx#gx-control

"Need every ounce of power your machine can give you? No need to close your browser. GX Control lets you set limits on how much RAM, CPU and network usage your browser takes up."