When using the "limited to designated sites" setting you have to wait for every tab to time out before you can add it to the container.
Also the possibility to use wildcards in the URLs would be a minimum requirement to make it usable for a developer.

Essa extensão funciona bem e é em geral prática de ser usada. Aparenta melhorar a privacidade durante o uso de forma adequada.

A extensão é ótima, funciona muito bem, outros navegadores concorrentes não tem uma extensão como essa gratuita. Os diferentes contêineres são facilmente identificados, evitando confusões.

I'm completely satisfied with this extension. It allows to keep multiple sessions (i.e. session cookies) to the same website thus allowing multiple logins. As a developer I use this for verifying the functionality of webapps that have multiple roles. Thus extension fully replaces SessionBox that was available on Chrome and now no longer works. Thank you.

Simple, intuitive, works seamlessly. My main use case is to isolate IBM product administration consoles.

Separating FB from Instagram is tricky (Have the Facebook container extension too, that comes default with FF). Since it wants to always open those websites in the container. Managed to separate them the first time but somehow it kept erasing the Instagram session at every restart of the browser, didn't know how to restore that so had to nuke the container and start over.