Gregory's Server@kurtseifried @kevinrns @ghorwood Firefox currently has containers. They're not quite the same as profiles, but they're in some ways more flexible, since you can control them on a per-tab basis.
For some reason, they choose to ship this functionality in an extension. I don't really know why.
https://addons.mozilla.org/en-US/firefox/addon/multi-account-containers/
@mitchellmebane @kurtseifried Containers are the best. Can have multiple Microsoft/Google tabs right next to each in different accounts, and set stuff like Facebook to only open it its own sandboxed container.
Use profiles still in Chrome, but haven't used Firefox profiles for years now.