Yes, Firefox has an option to clear this data. To check whether you enabled it: Open the Settings page, switch to the Privacy & Security panel, and scroll down to the History section. If it isn't already, change the selector to: '''Firefox will: Use custom settings for history''' Here are the two problem settings: '''(1)''' "Always use private browsing mode" Site exceptions cannot be saved to disk in this mode. '''(2)''' "Clear history when Firefox closes" PLUS when you click the "Settings..." button to check details, a check in the box for "Site settings" - that combination will clear your exception lists at shutdown. Can you make sure those are turned off?