You still need an extension to automatically open specific sites in their own containers. I genuinely don’t get why.

Damn, that’s another thing about Firefox that absolutely drives me crazy. They implement some feature as an extension, then they include it with the browser by default and just leave the extension there for some reason. It’s the exact same thing with Firefox translations, it’s integrated into the browser now but they still have an extension https://addons.mozilla.org/en-US/firefox/addon/firefox-translations/