A long time ago, I discovered that when I signed-in to a website in a Private Window, I would remain signed in to that same website in a different Private Window. I realized that all private tabs belong to one Container.
Perhaps there should be a container for each Private Window. After all, there is a certain logic built into windows so that you can separate your different tabs and browsing activity in different windows. It therefore makes sense that if you access the same website from different Private Windows, it would be for different reasons and different use-cases, and we wouldn't have the same need, therefore the website shouldn't have to access the data it already has stored on Firefox. And while this rationale doesn't make it necessarily more preferable than the status quo, there would also be a Privacy benefit from making this change: it would strengthen Firefox's powerful container abilities, by isolating websites and their data, separating more privacy-invading websites from others, while still keeping the features and functions of Private browsing for all those tabs.