Nice to know about that. Odd that it doesn't list any of my existing profiles though
You're right, it seems both the UI and the old about:profiles page do use the same underlying implementation, but the UI does not pick up any profiles added through the about: page. If you create a new profile from the UI, that will show up in about (after a restart).
It blows my mind.
I can't have profile without having a "Sign In" button in my toolbar. Mozilla… please. How is it possible, to ship a feature and do that…
I mean, I've been using about:profiles for ages, but it would definitely be nice to have a bit more polish (e.g. every now and again I forget that a newly created profile is automatically promoted to default)
[edit] well seems I have to eat my words - there's a switch in about:config named "browser.profiles.enabled" that toggles a profiles menu item with some UI that apparently has existed for years. Nice!