does the job! Improvement would be to create a new container tab from the context menu of a tab (right click on tab-title)

Excellent.

I've found Containerise to be a way better addon than this.
MAC for me takes like 10 seconds to load the menu, Containerise opens instantly.
Adding a website to a particular container is quite an annoying process, since you need to scroll the container list, and there can be dozens of containers there if you use Temp Containers addon.
Meanwhile, in Containerise adding it is very easy - you can even edit the config in form of text directly, you can also import/export the config in the same way, as plain text.

A fundamental feature

It's hard to give a review for this, because the effect can be hard to see. However, being able to separate different websites into different containers is really useful for when I'm multi-tasking and trying to use multiple accounts at one time.

Also, I think I've noticed less scarily intrusive and stalking ads after separating the accounts and cookies into different containers.

Very convenient

I use containers as a separation of work areas so that I can switch between work and entertainment so that unnecessary tabs don't distract me. Containers don't do that well!

1) I want the containers to be easier to hide. Right now the interface is complicated, there are a lot of clicks.
2) It's not clear why a hidden container drops me all the tabs in it if I add a new tab to the container. I just want to add a tab, not open 100 tabs I don't need!
3) I see the concept of containers as switching different desktops. So that they don't mix with each other unnecessarily.
4) Tabs outside of containers. There should be a setting that specifies what to do with these tabs: either hide them when any container is open, or leave them parallel to the container.