Well I don't. They are planning to spy on their users too:

• https://www.ghacks.net/2017/08/22/mozilla-plans-to-collect-anonymous-firefox-browsing-data/

Fortunately, Firefox is still the most transparent browser out there, and there is a transparent opt-out as always, however the tracking features are enabled by default. So novice users who don't add this custom user.js file (which was already updated to disable this), are being spied upon by default.

I can't even imagine what is inside Google Chrome, that is why I only run it inside a VM.