[qwerty456127]

Although I use Cookie AutoDelete and open GMail (which I didn't whitelist) in a separate container, GMail still remembers me somehow. I have to manually go and clear all the saved data in the Firefox settings to actually reset everything.

[bostonvaulter2]

It sounds like you're hitting a Firefox bug affecting Cookie AutoDelete. Something about the recent changes to cookies has prevented extensions from clearing partitioned cookies.