Zen supports the add-ons and extensions from FF. (Source: been using it for about a month)

While like other have said, extensions do work, I wouldn’t expect zen to prioritize extension compatibility. I’ve been following development and it seems like a personal project

It would be good for them to make sure it’s clear that it’s a fork of Firefox and supports addons in their marketing! Right now it’s quite a ways down the home page.

Zen is a fork of Firefox, supports Firefox extensions, and retains the built-in access to the Mozilla extension/theme stores from vanilla Firefox. If you go to install an addon, it even gives a popup to “Add to Firefox”.

It’s a good browser with only minor issues. I’m on Win10; automatic updates don’t always succeed, and it seems like it blocks some communication between the 1password desktop app and the browser extension because I have to sign into each separately. Otherwise, I prefer it to Firefox in pretty much every way.