The purpose of browser extensions is to build up an install base then sell out to some corporation that then promptly leverages that user base to exfiltrate data and monetize it.

No thanks. They should have to declare to the browser what it is they want done instead.

And extensions do exactly that in Firefox. When installing (or updating) extensions you're notified of any and all permissions the extension is requesting from the browser and you're given the choice to proceed with the installation or not. Google goes a step further and just straight up denies user choice entirely.

This point would be far more credible if browsers weren't in business to do what you claimed extensions are there to do.

I'd also argue that creating a full browser without a profit motive is more unrealistic than creating an extension and uploading it - for free - to a web store.

I think you're confusing the extension and the browser. The browsers are generally in the business of supporting an advertising company.

It still sounds like you don't want browser extensions then.

... But they do that. The declaration is written in a language called JavaScript.