You would think but no. Open a private window and log into a site. Then open another and it’ll be logged in. Incognito windows share cookies. They are deleted once incognito mode is turned off but that doesn’t help us in our “open 100 windows at the same time to get a bunch of slots” use case here.

Ah OK, I am coming from Safari background, where each private tab is isolated. Do you know why would Firefox make it differently by default?

Both chrome and Firefox do it. No clue why! I don’t have a mac to validate that on desktop safari. Firefox has these containers for isolation