How to Firefox in Private mode?

See https://support.mozilla.org/en-US/kb/private-browsing-use-firefox-without-history

I just press Ctrl+Shift+P and a private window opens, you can tell it by the purple mask icon in the corner. You can also open it from the menu in the top right, New Private Window. If you want Firefox to always open that way, turn on Always use private browsing mode under Settings, Privacy and Security.