That is normal. What private mode does is keep your history/tabs/cookies/etc. in memory rather than writing them to disk. See: * [[Private Browsing - Use Firefox without saving history]] * [[Common Myths about Private Browsing]] If you want to be able to resume use of private tabs automatically, you probably need to use an add-on to store them. Or if you want more control, you could allow Firefox to write some data to disk but clear it by hand from time to time.