Generally speaking, Container Tabs try to make you look towards the internet like several users while on your end it behaves like a single-user experience. So,

Generally speaking, Container Tabs try to make you look towards the internet like several users while on your end it behaves like a single-user experience. So, things like history, bookmarks and add-ons are not separated by Container Tabs. And the technology behind this was developed by the Tor Browser devs and then uplifted into Firefox and reused for this, so this is a proper security/privacy feature, not something that only works on the surface.