[BrendanEich]

I don't have measurements, as noted (others should chime in), but it matters not only in time to get to extension page process or tab process -- C++ in same process vs. JS after C++ across process boundary matters in memory use terms too, direct (allocation) and indirect (cache effects).

I've been doing browsers since JS was super-slow, advocated its use in Mozilla XUL UX back in the day without it being an issue _per se_, watched JITting JS engines make it even less of an issue for such 10Hz or even 60fps deadlines when done right -- but C++ over JS and in same process vs. multiprocess matters for blocking, due in large part to how many requests there are, and how they affect page rendering.

We are benchmarking again now that we have staff, so I'll try to update here if I do get any results. I don't believe we are yet testing vs. uBO+Chrome, though, for the reason given. We are allies.