Buggy GUI. I click Add, then menu stays small the same, doesn't resize, I can't see what options it shows. Doesn't work.

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?