The Feature I Most Want in Web Browsers

Firefox already has native cookie blocking with the ability to add your chosen sites to an allow list, and JavaScript can be blocked, again with an allow list, using add-ons like NoScript, uBlock Origin, or uMatrix.

It looks like Chromium has native cookie blocking with an allow list as well.

Firefox: about:preferences#privacy

Chromium: chrome://settings/content/cookies

Absolutely. Blacklist it all (most).

Worst decision browsers made was allowing third-party Javascript.

Easy to blacklist it on Android.

Brave has an easy JS toggle on Android. Brent is iOS, don't know if iOS has the toggle.

I block third-party JS with uBlock on desktop. If there was a better toggle available, I'd blacklist all by default.