In private browsing mode you get a separate cookie jar, so if the website would recognize you in normal mode via a special cookie then this cookie isn't send and you would have to login once again to Google Analytic. ----- Firefox uses two independent cookie jars, one for normal mode and a second one for Private Browsing mode that is shared amongst all PB mode tabs and windows. Cookies used in a PB mode window tabs are kept in memory in a separate cookie jar just like other session data is kept in memory in PB mode, so a website won't recognize you. Cookies saved in normal mode can't be accessed as they are stored in a different cookie jar. The PB mode cookie jar is cleared when all PB mode windows and tabs are closed.