Excellent Add-on, exactly did what I was looking for all over the internet!! this function is missing in the original multi-container extension. Thank you, Kirill.

Hi Kirill, this is an excellent add-on. Please keep working on it. It's very useful. I hope more people find and use this nice add-on. This feature is very helpful !!

it's not perfect, there are bugs to kill (and browsers limits to accept). still great, exactly what should be integrated in mozilla's product by default

It works, but has a troublesome side effect where tabs that are configured to open in a specific non-default container are duplicated into two tabs.