it works great BUT I can only partially access the 'Manage Containers' screen to customize or edit existing container or add a new one, the 'Save' button is not visible. The "manage container' button on the previous screen is barely visible.

This does not work for me anymore, does not open the urls in the new containers as it should. Something has been broken for a few firefox versions now.

Still no manual adding of URL's !
Workaround here:
https://github.com/mozilla/multi-account-containers/pull/2114#issuecomment-1004056712

Good tool for security and dealing with numerous accounts when performing administration for a group of clients.

please add a similar extension for managing profiles , not for individual tabs but whole browser, like on chromium based browser

Just new for me, but it seems interesting.

Instead of open many windows like Chrome, this extension make me feel a bit control because it's happened in ONLY ONE windows.

Only gripe I have is when a site has separate sites to go to before it comes back to the main site. Ends up in a loop back and forth to each site, hence it never goes to where I need. End up needing to remove a site from containers completely, just to view a page. A remedy would be to allow us to enter an address into the add-on manually that will put it into the container.

This is a must have for me and the reason I still use Firefox. The ability to have my email open in one tab and my administrator account in another tab is just one example of why I love this extension. All web browsers should support this by default.