There are pros and cons to that though. It can be useful to have extensions unique to each profile.

Firefox has had those kind of profiles for a long time, they just aren't the most accessible thing in the world. But yeah, you can access them from about:profiles or also via the command-line with "firefox -P". If you want to use it more extensively, there's also extensions available for easy switching, like for example Profilist. https://addons.mozilla.org/en-US/firefox/addon/profilist/