OK, so the feature I have been using in Chrome (Profiles) and that I thought I was missing in FF, won't ever exist in FF. Because, Multi-Account Containers (https://addons.mozilla.org/en-US/firefox/addon/multi-account...). I guess I just needed to know that this was a thing and that it had another name. Going to try to now totally forego Chrome. Thanks for the discussion under https://news.ycombinator.com/item?id=21498452 that made me realize this was a thing.