I am a heavy user of Firefox Profiles. In fact, I maintain a script to make Firefox behave better on KDE Plasma in a multi-Activity set-up, which relies on Firefox Profiles.
So I was quite excited to learn that handling profiles should now be better.
But when I open the new profile manager from the hamburger menu, I don’t see any of my existing profiles.
I’m also concerned like you and wonder why they are not integrated. It looks like now they are more integrated process-wise, without true separation. More efficient for memory and processes quantity maybe. I might be wrong. It wasn’t a problem on my side with 2 or 3 profiles running at all time.