Private Browsing mode is designed to not keep take of your browsing history. This allows users to browse the internet without their history from being saved on their computer. Because of this, you cannot restore a session that was done in Private Browsing mode, as the session is permanently deleted when Firefox is closed. If you would like to have the ability to restore previous sessions, please use Firefox in regular browsing mode. For additional information about Firefox Private Browsing, please read this Mozilla support article: *[[Private Browsing - Use Firefox without saving history]]