Hello. Right now, Firefox supports various sidebars like the Bookmark sidebar, History sidebar, etc. I think it would be incredibly convenient to add a Containers sidebar as well.
Just like the Bookmarks sidebar, you can bring it up with a keyboard shortcut, it allows you to view, manage, rearrange, edit, delete, etc. your containers, and it allows you to transfer the current tab to a container.
Basically it's like the Firefox Multi-Account Containers floating panel that shows up when you click on the containers button on the toolbar, but permanently pinned to the side of the browser.