This is a killer feature that I would love to see incorporated into Firefox proper. I started using it fairly early on after its release, and containers quickly became integral to how I browse. If you want to be simultaneously logged into multiple accounts for the same website easily (and even restrict how such a site can relate your activity across those accounts), this is the extension for you.

好啊

Very useful if you have multiple accounts for different sites. I use it all the time!

It'd be nice to be able to open in a new tab based on URL matching, not just domain

Très pratique pour séparer les sphères d'activité.

Fonctionne très bien à date, très pratique à différents niveau, par exemple, pour pouvoir tester des sites avec différents niveau d'accès simultanément.