I lived through the firefox extension debacle in 2019 or so when FF accidentally let a cert expire and it helpfully uninstalled all my "unverified" extensions, of which container tabs was one. When everything was fixed, my settings were erased.
Except they weren't. To this day, I still get random ghost-like behaviour from my old container tabs settings. Google-contained apps will try to open in my banking container, as I gradually realise all of my containers were deleted but the URL-to-container mapping wasn't, and it was by ID not name, and the IDs have been reused.
Containers should be a core feature because they are /the/ feature ff has over the chrome army right now. I know they were (are?) trying to prove that core features aren't necessary because you can write anything in a web extension (IIRC that's how they justified getting rid of RSS), but it just hasn't been so in my experience.