According to the upstream documentation (https://developer.mozilla.org/fr/docs/Mozilla/Command_Line_Options#-private), "-private" is to initially open firefox in private browsing mode, whereas "-private-window URL" is to open the URL in a new private window when a firefox instance is already running.
The man page is outdated (it's missing documentation for "-private- window"), this is tracked by bug #1734975. ** Changed in: firefox (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1835650 Title: firefox fails to open private sessions from bash To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1835650/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs