Pick your battles... easier to cherrypick your own stuff on top of already existing codebase. At least you need to worry only about a small patchset rather than own rendering and js engine just for a very abstract concept of "avoiding monoculture", and instead of focusing on CSS rules and JS optimization and whatnot, you can focus on things that matter for your goals

it's not my fight though. If Mozilla thinks burning all these resources on their own engine is a good thing then, burn ahead. there are worst things to burn money on in the end. and it's not my money...

At least rust came out of all that.