I know I'm a bit late with my reply, but I don't follow hacker news all too much. That said, in general, IPC is slower than threading for the simple reason tha

I know I'm a bit late with my reply, but I don't follow hacker news all too much. That said, in general, IPC is slower than threading for the simple reason that processes are in different address spaces. When you perform an IPC call, you must take a TLB hit. With communication between threads, there is only context switching overhead (assuming no preemption between calls.) Chrome has a few different ways to do tab communication, none of which are truly "one process per tab".