[nijave]

You'd still have to MITM HTTPS which is non-trivial (compared to installing an extension) and accept the risks of managing your own CA

Afaik uBlock benefits from some browser APIs that can do things like prevent content from loading before the add-on is injected into the page so you'd lose some coverage there. I imagine it'd also be fairly difficult to intercept all outgoing web requests (to selectively block them) which a browser is fairly well positioned to provide an API for.