This is a great app and works very nicely with how various sites redirect you to their sub domains etc. The only thing I'd like added is
(1) being able to delete cookies and cache for a container group
(2) being able to assign different containers not only for different sub-domains, but different URI's

Not bad. The only question I would have is - can you have wildcards for "always open *.example.com" in container XYZ?

Absolutely necessary extension thanks! The only thing I wish would be to have entire windows automatically opening new tabs in the container of the other tabs of the window

Very useful

I love the idea of this add-on. It is a browser-defining feature that is a big reason why I am a loyal Firefox user.

But, it pains me to write this--Multi-Account Containers is _extremely_ buggy. The add-on crashes constantly (closing all of your container tabs and deleting all your custom containers), sometimes containers are mysteriously duplicated hundreds or thousands of times, sometimes it forgets which sites are assigned to which containers (forcing you to reconfigure them). At one point I had to delete my Firefox account, losing a paid subscription to Mozilla VPN, because MAC had corrupted my sync settings. BTW there are >700 open issues reported on GitHub: https://github.com/mozilla/multi-account-containers/issues.

But--despite being a buggy mess, I still love this add-on for what it does when it works, and for what it could be one day. So I can't give it anything less than 3 stars.

This is add-on is not only amazing, it is essential.
I use it for two reasons:
1. The massive privacy boost.
2. The ability to separate my work and private life. I also use containers for finance and shopping.
Before this add-on I would have to either use a second browser and log-in to different accounts in private mode.
I love this add-on.

the main reason why I prefer Firefox to any other browser

Having separate cookies for each container is an absolute godsend!
The thing I really miss is, that you aren't able to set containers in bookmarks, that's why I deducted a star.

On YouTube, I have a container for each of my channels, so I don't have to switch accounts constantly, and each container is saved as a separate bookmark, so I can access that channel easily.

For the time being I installed a separate extension to solve this, but imho, this should definitely be solved in this extension, since this is a very basic/common request I would imagine.
https://addons.mozilla.org/en-US/firefox/addon/container_bookmarks/