Works as advertised. I have 6 different email accounts for personal and business accounts and it's been a pain to have them all available without interfering with each other. Containers works great to keep them separate. I added in Simple Tab Groups to gain a little more functionality and they work well together.

Could have better UX but one of the most underrated extensions.

For some time (Debian, 115.5.0esr) the Google Translate and Google Maps pages do not open in the google container I created, but actually in any container, and only open without using a container. (https://translate.google.hu/ ; https://www.google.hu/maps/) I see this, on new and new pages: Before moving on to Google... | Are you opening this website in the assigned container? continuously and endles. Enhanced Tracking Protection is still the stronger setting. There is no problem with the YouTube page. What is the explanation for this?
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Update
Today I tried to set the value of privacy.userContext.enabled true to false in the about:config settings, and then I opened the Google Translate and Maps pages without a container (after all, I turned it off). I then set privacy.userContext.enabled back to true and the two web pages now open in the Google container I created. It's fixed the problem. After all that, I set the two websites to always open in this container. I don't know what the cause of the problem was, but I'm glad it's fine now. Cheers up. :)
https://support.mozilla.org/hu/kb/kontenerlapok

This add-on should be good but is knee capped but extremely poor support. The lack of options to manually add sites to the "Always Open In" listing can make it impossible to log into some sites. It NEEDS to have this feature along with wildcard support in the listing.This issue has been known about for over 5 years but is still outstanding.

Would not recommend this plugin to any one

Useful for me

Flawless so far, the UI is particularly elegant.