I guess it can be fast, but it cannot be the same as the web is meant to run untrusted code, so all the security and privacy features that are essentially requi

I guess it can be fast, but it cannot be the same as the web is meant to run untrusted code, so all the security and privacy features that are essentially requirements will cause an overhead, and not using the systems's preferred rendering methods might also incur in some penalties, at least just not sharing memory with all the other programs (maybe it doesn't matter today now that all programs are Chrome in a trench coat). Didn't Firefox recently removed a hack where an invisible animation was running at 60Hz and forced repainting? I'm assuming that being closer to the host's systems won't run into such workarounds and penalties of using web technologies. I'm guessing that XUL also resulted in using an abstraction layer on top, but at least it was probably considered trusted and ran faster (at least is old enough that it doesn't require having 16GB of memory)