Unintuitively, you want to have no default set for that domain, and you want to open an empty tab of that container type (by long clicking the new tab button or

Unintuitively, you want to have no default set for that domain, and you want to open an empty tab of that container type (by long clicking the new tab button or clicking the container addon button itself to get a list). Once you have a container open, middle-clicking the new tab button will open an empty tab in that container. I agree that the UX is horrendous. Most of that is a byproduct of implementing it as an addon instead of a feature.