Seems to work great so far, but I have a few suggestions.

Currently it doesn't appear that your settings sync between devices. I've got FireFox installed on both my work computer and my home computer, logged in on my personal email and everything synced between the two. I spent some time last night setting up my containers, and setting certain sites to only open in specific containers, etc. When I logged in on my work laptop, it shows all the original containers (none of the new ones I setup), and when I visit certain sites, they don't default to the container I configured on my home computer. This functionality would be great to have.

Another suggestion would be able to move an existing tab/site into a container. When I installed the addon, I had several tabs open. I had to open a specific container tab, then copy/paste the URL from the generic tab, to the container tab. It also doesn't appear to let you move the tab from one container to another.

I'm still getting used to the addon, so maybe this little nuances aren't as big of a deal, especially as I setup some default behaviors, but for me the biggest thing would be addon settings/containers syncing across browsers.

Edit: Oh, once you get the syncing of settings across devices, enabling this addon for mobile use would be awesome.