Compartments are similar in many ways, but also very different. Both processes and compartments shield JavaScript objects against each other.

The most important distinction is that processes offer a stronger separation enforced by the processor hardware, while compartments offer a pure software guarantee. However, on the upside compartments allow much more efficient cross compartment communication that processes code.

With compartments cross origin websites can still communicate with each other with a small overhead (governed by certain cross origin access policy), while with processes cross-process JavaScript object access is either impossible or extremely expensive.

In a modern browser you will likely see both forms of separation being applied. Two web sites that never have to talk to each other can live in separate processes, while cross origin websites that do want to communicate can use compartments to enhance security and performance."

You can read more about how that works at http://andreasgal.com/2010/10/13/compartments/

Weird; I switched from FF to Chrome specifically because FF was a huge memory hog. I have read that it is better these days though.

-- what does the downvoting mean here exactly? That I didn't experience excessive memory usage in FF and I'm lying?

Yup, it does. My problem with FF years ago was with leaks. It would eventually bring my entire system to a state of paging hell until I killed it. That was years ago though, I've since become comfortable with chrome and haven't found aneed to go back.