I’m not actually sure that the problem is with cookies. On Zorin, neither Chromium-browser nor Firefox will allow be to switch back and forth between 2 yahoo mail accounts. I must enter the the passwords every time. This does not happen on my Windows machine. I have Remember Me on the Yahoo page checked. I have options in the browsers set to save cookies from session to session.
In Firefox Privacy & Security settings, Manage Data, it says that data from websites in the following list are only deleted when space is needed. This is a new Zorin 15.3 install with 16 gigs of RAM and 1T of m.2 storage. It should have plenty of space. mail.yahoo.com is listed in this section.
In Firefox Exceptions – Cookies and Site Data, http://yahoo.com is listed as ALLOW.
During my testing they are not running in firejail. I invoke them like this in a terminal:
What am I missing?
Note that I am not using either browser as a password manager.