[pcwalton]

> There is no way Firefox can guarantee anywhere near the level of stability and security Chrome offers without a process per tab.

It has no security benefit without Site Isolation (which isn't unconditionally a process per origin either for performance reasons). In both Chrome and Firefox, any site can embed another cross-origin site in an iframe, and it will share a process (and a main thread).

Chrome does not use an unconditional process per tab. Nobody would.

[AgentME]

I believe Chrome is moving to having cross-domain iframes in separate processes. I remember seeing a flag for it.

[pcwalton]

Not for all sites unconditionally, only for those that opt into site isolation or are high value. Too many sites have tons of iframes to do otherwise.