$ firefox --help
Usage: /usr/lib/firefox/firefox [ options ... ] [URL]
       where options include:

X11 options
  --display=DISPLAY  X display to use
  --sync             Make X calls synchronous
  --g-fatal-warnings Make all warnings fatal

Firefox options
  -h or -help        Print this message.
  -v or -version     Print Firefox version.
  -P <profile>       Start with <profile>.
  -migration         Start with migration wizard.
  -ProfileManager    Start with ProfileManager.
  -no-remote         Do not accept or send remote commands; implies -new-instance.
  -new-instance      Open new instance, not a new window in running instance.
  -UILocale <locale> Start with <locale> resources as UI Locale.
  -safe-mode         Disables extensions and themes for this session.
  -jsconsole         Open the Error console.
  -browser           Open a browser window.
  -new-window  <url> Open <url> in a new window.
  -new-tab     <url> Open <url> in a new tab.
  -preferences       Open Preferences dialog.
  -search     <term> Search <term> with your default search engine.
  -private           Enable private browsing mode.
  -private-toggle    Toggle private browsing mode.
  -setDefaultBrowser Set this app as the default browser.