What is your strategy with updates? Do you give yourself permission to write to opt or do you run Firefox Nightly as root once a day so it can update iself? I tried the latter for a few weeks and grew tired. I can't wait for containers to come to Firefox stable (which is the feature I am looking forward to the most in nightly).
But you might want to consider a different distro with more up-to-date packages anyways.
It'll be consistently tested with those more up-to-date packages, so would most likely be more stable than your attempt to rejuvenate Ubuntu LTS or whatever distro you're using exactly.