To open a bookmark in a specific container: right click the bookmark and select the container in the new option added by this add-on. Very useful.

This stupidly simple button is all I needed. Thnx.

Very useful idea, because default Multi-Account Containers button is too slow and contain many unnecessary elements, so thanks for developing! But after installing extension on Firefox 62 - I see no button shown in panel, also I can't find it in customization list. How can I find and add this extension button?