I've been using Firefox profiles for years, never had an issue with them, the UI, or how to access the functionality. Sure it wasn't immediately easy to find and use but I never really got a lot of the criticism. Coloured themes (which them seem to be integrating) was an easy way to differentiate the profile I was using, especially when I had multiple open at once.

Glad it's getting an update, hope it doesn't ruin a decent feature.