Even better, type "about:profiles" into your URL bar, create a new profile that runs in an entirely separate Firefox process, and live your second life there.
When an update is applied between the first and second profile process, any new tab won't do anything in any of the instances. Firefox likely still doesn't detect this state.
Edit: That is, if you use Firefox with two or more profiles, and may start one profile later (after a new update was published).
It's an underrated feature, IMO. Profiles can be made very purpose-specific, and I like that there's not the possibility of leakage due to a site exploiting an add-on sharing data across containers, etc. I still like the mukti-containers feature, but I see it as less of an anonymity thing and more as a convenient way to be able to sign into multiple website accounts at once.