While I'm not thrilled Mozilla ran an experiment placing ads in the browser, I am confident that anything they release will be easy to disable via about:config or some other configuration.

However, looking closer at this situation there is a bit of a troubling fact that `experiments.enabled` - the configuration directive used here - doesn't appear in about:config but certainly is being used:

https://dxr.mozilla.org/mozilla-esr45/source/browser/experim...

Looks like someone filed a bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1517147