[FBT]

With profiles, each profile has it's own history, bookmarks, browser settings, and so forth. In effect, it's a separate instance of Firefox.

Sometimes that's what you want, and profiles certainly aren't going anywhere. But the idea behind Containers is just that you can be logged in to separate accounts simultaneously in multiple containers.

In practice, that means a better and more convenient UI. Containers work on a per-tab basis, so you can have multiple tabs logged in to the same account right next to each other, instead of in different Firefox processes. Plus, you can right click on a link and select "Open in New Container Tab".

So while Containers are more than a UI on top of Profiles, it practice one of the main advantages is the convenience of the UI.