[mikeratcliffe]

Firefox uses compartments per domain instead, which is a great alternative to process per tab: "Some readers might wonder how compartments compare to per-tab processes as they are used by Google Chrome and Internet Explorer.

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/