I found these 2 cmds and they work for me with my distro(openSUSE Tumbleweed)version of Firefox. see screenshot

firefox --new-window 'http://www.google.com' firefox --new-tab 'http://www.google.com'

Hmmm...??? Thanks but doesn't work on OSX Unix terminal zsh The URL needs double quotes Tried lots of variations but it just returns:-

Me@My-iMac % open -a firefox --new-window "http://www.google.com" open: unrecognized option `--new-window' Usage: open [-e] [-t] [-f] [-W] [-R] [-n] [-g] [-h] [-s <partial SDK name>][-b <bundle identifier>] [-a <application>] [filenames] [--args arguments] Help: Open opens files from a shell.

     By default, opens each file using the default application for that file.  
     If the file is in the form of a URL, the file will be opened as a URL.

Options:

     -a                    Opens with the specified application.
     -b                    Opens with the specified application bundle identifier.
     -e                    Opens with TextEdit.
     -t                    Opens with default text editor.
     -f                    Reads input from standard input and opens with TextEdit.
     -F  --fresh           Launches the app fresh, that is, without restoring windows. Saved persistent state is lost, excluding Untitled documents.
     -R, --reveal          Selects in the Finder instead of opening.
     -W, --wait-apps       Blocks until the used applications are closed (even if they were already running).
         --args            All remaining arguments are passed in argv to the application's main() function instead of opened.
     -n, --new             Open a new instance of the application even if one is already running.
     -j, --hide            Launches the app hidden.
     -g, --background      Does not bring the application to the foreground.
     -h, --header          Searches header file locations for headers matching the given filenames, and opens them.
     -s                    For -h, the SDK to use; if supplied, only SDKs whose names contain the argument value are searched.
                           Otherwise the highest versioned SDK in each platform is used.
     -i, --stdin  PATH     Launches the application with stdin connected to PATH; defaults to /dev/null
     -o, --stdout PATH     Launches the application with /dev/stdout connected to PATH; 
         --stderr PATH     Launches the application with /dev/stderr connected to PATH to
         --env    VAR      Add an enviroment variable to the launched process, where VAR is formatted AAA=foo or just AAA for a null string value.

open -a firefox -W --args --new-window "http://www.google.com"

---pulls firefox to foreground but nothing else - and Unix just wait until ^Z

I figured it wouldn't work in UNIX. I use tcsh, but it also worked for me in zsh. Good luck