Limiting resources sounds cool. I wish I could at least determine why Firefox sometimes goes out of control eating everything. Setting a resource limit per page would be good too. Sometimes my whole computer is ground to a halt, but closing a single tab fixes it. Often not a page that is obviously doing much. Certain ecommerce sites are frequent culprits. Doing something in the background.

Firefox can tile two pages now: https://blog.mozilla.org/en/firefox/split-view/