Add-ons that store or otherwise handle browsing data must support <a href="https://developer.mozilla.org/En/Supporting_private_browsing_mode">Private Browsing Mode</a>. During a Private Browsing session, no browsing data can be written to disk, and all of this data must be cleared when Firefox quits or the Private Browsing session ends.
Add-ons that store or otherwise handle browsing data must support <a href="https://developer.mozilla.org/En/Supporting_private_browsing_mode">Private Browsing Mode</a>.  During a Private Browsing session, no browsing data can be written to disc, and all of this data must be cleared when Firefox quits or the Private Browsing session ends.