Extremely handy! Like having a private browsing window on steroids.

Firstly, if you are not using Mozilla Firefox as your default browser, you need to see the light! But, idioms aside, the Multi Account Container Add on is a great and easy to use bit of kit. Basically, little sandboxed tabs that keep everything seperate so you can log in, if wanted, to multiple accounts on the same platform. This may be facebook, Gumtree, Amazon etc. Great and thank you all at Mozilla - please continue to help keep the internet inpartial and out of the hands of the greedy corporate b******s that try to steal my life at every click of the mouse. Happy User

Muy conveniente para hacer pruebas con diferentes usuarios en una aplicaciones web.

コンテナーという形式で複垢ができます。
コンテナごとにタブは色分けされており一目瞭然。
また、あるコンテナの全タブに対して新しいウィンドウで開くとか、隠す（一旦閉じて、あとで開けるようにする）機能が「あとで読む」タブを一旦しまえるので地味に便利です。

This makes testing different user roles a lot easier compared to the two you would get with private mode + normal mod. Love it.

It's perfect at what it does.