The complete rewrite wasn't initially too good either. It took them years to bring it on par with Netscape 4.7, warts and all. I've been in a talk of a mozilla

The complete rewrite wasn't initially too good either. It took them years to bring it on par with Netscape 4.7, warts and all. I've been in a talk of a mozilla developer like a decade or more ago, shortly after they had released the rewrite. His comment on starting a project like that from scratch: "don't". What they intend to do (slowly and gradually transition to Servo) seems consistent with an organization that has learned from this experience.