I like the concept but wouldn’t use it.
If you run extensions, even discounting the hostile and inconvenient installation process, there is no mechanism to auto-update your extensions and if you are running a compromised version or one that now has serious privacy issues there’s no way you will even know about it unless you manually check each of your extensions regularly.
And without extensions, I’m not comfortable using any browser. Host-based ad and tracker blocking on my machine or at a DNS level isn’t good enough either.
Hardened firefox is still the best in my opinion.