Ensures your privacy and is recommended by Mozilla

One of the most useful "features" of Firefox. I hope it becomes part of the standard browser one day!

Super simple to use with its clearly colorcoded tabs and UI actions, and good at what it promises: allowing multiple accounts on the same site in the same window (very useful when I need to switch between testing accounts for something I'm developing or trying out), and increasing privacy by containing your login and tracking cookies to the specific sites you use within the container without compromising convenience, as is the case with about:profiles.

Amazing plugin

Must have add-on for developers, power users, anyone who has multiple accounts on web sites / services, privacy conscious users and anyone who is aware of cookies and other more advanced tracking methods and want to keep activities separate (ex. Work, Personal, Development, Anonymous, etc.)

Really good extension for separation of concern :)

This extension was, originally, part of Firefox. I kind of understand the reasoning behind removing it and making it into an independent add-on (faster updating, independent development etc.), but I fear some day Firefox will drop it altogether, like it did with other technologies (let's not talk about WebSQL and the amazing beast that was XUL).

Anyway, this is an essential extension, full of features (don't forget to check its options for more essential features that come disabled by default, for whatever reason) and very light. There are lots of reasons for not leaving Firefox for other browsers, and this is surely one of them!

Imagine that you admin lot of accounts. Containers made life easier.

This is the key reason I will never stop using Firefox. Such an underrated feature.