[grishka]

IMO most of the complexity of modern browsers is in all those strictly optional, app-like features. PWAs, service workers, JS JIT and all that stuff. If you want to build just a hypertext viewer, not a full-fledged OS/application environment, just leave them out and nothing of value will break. Things also become substantially simpler if you aren't looking to make your JS execution as performant as theoretically possible (and you don't really need to with how most websites actually use JS).