suggestions:
1- organizing the containers in folders and sub-folders structure: I don't use it as much because I manage many accounts, and it would be nice to have the option to create folders. For example: you would have a folder called "Others accounts" and in it there is two folders "Managed businesses" and "family." Inside "Managed businesses" folder you would have business1, business2 etc.

2- adding description to containers and viewing them when hovering over them

3- have more custom control on colors and icons of containers, let the community make icons which could be added within the add-on

4- domain specific containers, example FACEBOOK.com

5- having two check marks; ☑ Always open this website/URL (Facebook.com) with this container (My Facebook) ☑ Except when I am in a different container.

Meaning if you made a container for a family member Gmail, Facebook, or their Other accounts; For example your mother, father, or technologically illiterate girlfriend accounts then you would be able to protect your privacy on ANY site not just Facebook, and manage other people or your other accounts.


Edit:

6- when long pressed the search bar or the arrow key in the Address bar button you can search or navigate to a site with a specific container