User Agent: Mozilla/5.0 (Windows NT 6.1; rv:10.0) Gecko/20100101 Firefox/10.0 Steps to reproduce: Tried to launch Firefox in a safe mode, but couldn't remember a command. It is necessary, that in case of firefox.exe /? or --help was shown a window with commands.

https://developer.mozilla.org/en-US/docs/Command_Line_Options List of commands: firefox /? | more "Print the list of all available command line options. Note that on Windows this only works with a redirection such as |more (bug 355889). This option is available only in a command console." You can launch/boot into safe mode with: firefox -safe-mode

Let then the console output gives on /? or GUI-window as the majority of programs do.