How large is the overhead in reality? The binary code will be shared anyway as presumably it will mainly be located in a shared lib (to allow just this effect), then there's the per-process data which would otherwise be shared between the tabs - stuff like the menu items, window data/theme stuff, etc.

So how large would the extra overhead really be? I always thought the main disadvantage of using processes vs. threads is in communicating across them, which in this case shouldn't be a major thing as each "tab" would not really need to do much IPC.