All exceptions and permissions including for cookies are stored in permissions.sqlite in the profile folder, so you can possibly keep a backup of this file. I'm not aware of an extension that allows to export and import specific exceptions.

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Note that it usally best to create the exception for a top level domain instead of for a sub domain that might vary. Note that exceptions are part of the Site Preferences, so you lose exceptions if you clear the Site Preferences.

You can use these steps to make a website recognize and remember you:

• create a cookie allow exception with the proper protocol (https:// or http://) to make a website remember you

You can check that you aren't clearing important cookies.

• using "Delete cookies and site data when Firefox is closed" keeps cookies with an allow exception
• using "Clear history when Firefox closes" to clear cookies clears all cookies including cookies with an allow exception you may want to keep

• Options/Preferences -> Privacy & Security
  Cookies and Site Data: "Manage Exceptions/Permissions"

Hi cor-el, thanks a lot for your reply. I tried first to add pons.com to the allow list but that was not enough. The idea popped into my mind to look, which cookies this site would create, and I discovered that it created a cooky for de.pons.com and one for pons.com After adding both addresses the permission question stopped popping up. So I know for the future what to look for.