Great idea with serious usability issues. It's way too easy to accidentally open a new tab in the global container space. The addon should bind to Ctrl+T or provide it's own keyboard shortcut to open a new tab in the current container. Ctrl+. is too indirect. It's also annoying to have a delayed confirmation that a site should always open in a specific container after explicitly checking the "Always open in (container)" box. Finally, the "flicker" when opening a new tab that is set to always open in a certain container is bad. I think it's opening a normal tab, then closing it and opening a container tab? It's distracting and looks broken.