Finally. I know that profiles have been supported for a long time, but about:profiles wasn't that user friendly and on macOS, profiles could also mess your dock icon, wouldn't open in the foreground, etc. It wasn't a good experience.

I think the new profiles will cause some confusion (at least initially) because these profiles are not listed on the old about:profiles page and the old profiles are not listed on the new UI.

Still, a good improvement for me. I no longer need to use the dev/nightly channels or 3rd party browsers based on FF just to have different bookmarks/settings/extensions. I'll need a way to add old profiles to the new UI though.