This lets me compartmentalize my browsing. I can sandbox different domains so that data isn't shared between them. This feature should have been built into all browsers long ago. Given the currently weak state of online privacy, it's refreshing to use a browser and add-ons built by a company that cares. This add-on is simple to use, but I think it would be a little more intuitive if all actions were available through the drop-down accessed by clicking on the Multi-Account Containers icon. In any case, this will forever be a default add-on for me in all new Firefox installations.