Good & Useful.
Looks like Multi-Account + Tab Groups . & developed by Mozilla make me feel better than thirdparty .

But . If when I use this addon as Tab Groups .
It 's very inconvenient to change which container I want show only.
It will be better has a button on [container list] that I can make one be only show.
& even which 2 or more container to show or hide.
need it not go into the [tab list] to set it hide or show than come out one by one..

Now this addon do good job on Multi-Account .
But the TabHiding function is completely wasted cuz extremely inconvenient to use .