At first I thought that this was like tab groups. It really isn't. Multi-Account Containers are all about privacy. And sure, you can have two different Container tabs with different Whatsapp accounts, for example. But for me it's much more about keeping Google's prying eyes away from all the other stuff I am doing and minimizing my social media footprints.
This add-on could be your only reason to start using Firefox if you aren't yet.

The only two things on my wish list for this add-on are 1. more icons to choose from (or just using your own icons) and 2. more colors to choose from (or just entering your own color codes).