Open Firefox
Type about:config in address bar
Press Enter
Type browser.privatebrowsing.autostart in Search:
Right click browser.privatebrowsing.autostart and click Toggle (value will change to True)
Restart Firefox to apply settings
Alternate method
Click Menu
Click Options
Click Privacy
Click Drop Down Box next to Firefox will:
Choose Use custom settings for history
Select checkbox Always use private browsing mode
Click OK to restart FirefoxType about:config in address bar
Press Enter
Type browser.privatebrowsing.autostart in Search:
Right click browser.privatebrowsing.autostart and click Toggle (value will change to True)
Restart Firefox to apply settings
Alternate method
Click Menu
Click Options
Click Privacy
Click Drop Down Box next to Firefox will:
Choose Use custom settings for history
Select checkbox Always use private browsing mode