My golly this extension is giving me a headache. You see, I am trying my best to limit how many browsers I use to just one -- Chrome I believe purposely makes G Suite programs work better on Chrome (GMail, GDocs, etc.), while Edge has a very fast and sleek PDF reader, but Firefox... has THIS!!

This multi-account container is SO GOOD that it is the one thing that neither Chrome nor Edge have anything close to. For background, I have my personal account (for my social media, bills), a school account (assignments, documents, etc.), a junk account (i.e. for registering to a free anime streaming website), and lastly my business account which also gets busy. I used to lose my MIND having to sign in and out in different websites (E-mail, Office.com, Instagram, Twitter) or use an incognito mode, but this saves me SO MUCH TIME, and reduces the confusion I used to face, trying to remember different passwords or which account I am supposed to be using.

Thank you Mozilla. This app single-handedly makes Firefox a mainstay as one of my favorite browsers.

multiple google and office 360 accounts open at one - solved!

This is very handy when using multiple O365 accounts. Love it.

Different accounts use the same URL for the same website. There's no way to use this for multiple accounts unless the different accounts had different URL's. Or there need to be better instructions.

I like the purpose of this add-on, but gave it only 3 stars because it currently fails in its stated purpose to "Keep different kinds of browsing far away from each other ... ". It will automatically open a container when it detects a site assigned to it. However, once in a container, it will open websites in it that are not assigned to any container. I find that it's very easy to forget to manually open a new tab when going to a website not assigned to the container. When in a container and opening a website not assigned to it or another container, a new tab should be opened automatically for the new, unassigned website.

working great with multiple email accounts

It's usable I guess.
The main issues it has are:
1. when forcing a site to always load in a specific container, subdomains are never included. There should be a way to include them.
2. After setting a site to always open in a container, there's an extra dialogue that appears the next time you open that site, which can sometimes render the browser inoperable.
3. It requires a keybinding even if you don't want it to be set to anything.
4. You can't make it so certain sites load in the default container.