They're not highly visible, but there's quite a few paid extensions. Chrome used to have payments built into the Chrome Web Store before they deprecated it a few years ago (https://developer.chrome.com/docs/webstore/cws-payments-depr...).

You've always been able to add your own payment system. I sell a freeium extension with payments going through Paddle (I guessed Google might deprecate their payment system so didn't risk it!). Gumroad and Lemon Squeezy are other examples you could use, where they both have simple license key checking web APIs.

> problem is you can't sell them.

I actually make a living selling browser extensions in the iOS and Mac App Store. Apple users are willing to pay.

I used to sell my extension in the Chrome Web Store, until Google eliminated Chrome Web Store Payments (mentioned by another commenter). However, even with Google's payment system, my sales were extremely low; thus it wasn't worth my time to implement my own payment system in the Chrome Web Store.

Apparently Firefox also used to have a payment system for add-ons but eliminated it.

This is purely a choice by the browsers. Chrome and Firefox have chosen to demonetize extensions. Safari has chosen to monetize extensions.

Safari extensions are an exception here. They are distributed through the Mac OS App store, often as an optional part of a desktop App that can then be enabled within Safari.

is this really a problem? Being strictly open without monetization is a feature.

You can still open a Liberapay if you want

open a what?

https://en.wikipedia.org/wiki/Liberapay - Platform for recurring donations/OSS funding.

I use them for personal things