Hi atticmaker

Exceptions are part of the Site Preferences, so if you do not keep exceptions you created then you might be removing the SP.

In case you use "Clear history when Firefox closes" or otherwise clear history.

• do not clear the Cookies
• do not clear the Site Preferences

• Options/Preferences -> Privacy & Security
  Firefox will: "Use custom settings for history":
  [X] "Clear history when Firefox closes" -> Settings
• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox

• clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exception for password and other website specific data
• clearing "Cookies" will remove all selected cookies including cookies with an allow exception you may want to keep

Well I am lost. Your are telling me 'site preferences' include details of the individual sites and whether or not those sites should be accessed in the first place. This looks like two completely different sets of data! Exceptions is a list of whether any site is to be visited or not and the other details are about information needed on a site. If I want to ban visiting a site, I hardly want my computer to keep details related to an actual visit - but you are telling me that if I want Firefox to remember whether or not I want to visit a site then I must not clear site preferences and Firefox will keep everything about any sites I have visited.

Any exception you create is stored by Firefox. If you want to last such an exception across a session then you need to keep these exceptions and that means you need to keep the Site Preferences because otherwise you lose these exceptions and you need to repeat creating exceptions each time you start Firefox. The exceptions are stored in permissions.sqlite in the profile folder. There is other file content-prefs.sqlite that stores other website related data like the page zoom.