I did try that, but found that it still remembered site info for accounts I was logged in until fully I closed everything related to the firefox browser. So containers has been easiest solution except for the process of manually creating and then deleting ones I didn't need anymore beyond the one session.
I had used Temporary Containers, but it hasn't been updated since February 8, 2021. Not actively monitored for security by Mozilla either so stopped using it. That addon was a perfect experience though for what I wanted.