I have Firefox 3.6 installed on my OS X (10.6) box. I would like to open an URL in the running Firefox instance (in a new tab or window, no matter) from the command line. I tried several ways, neither switches -new-tab, -new-window, -url, or none helped me. I always get the A copy of Firefox is already open. Only one copy of Firefox can be open at a time. error message.

  • The exact same thing is happening for me with the same setup.
    – Toby
    Feb 26, 2010 at 16:32

2 Answers 2



open http://www.superuser.com

from the command line will (at least for me) open a new tab to superuser.com in firefox (which is my default browser)

  • 7
    open -a FireFox http://superuser.com if you have a different default browser
    – cobbal
    Feb 26, 2010 at 17:16
  • 1
    @cobbal, though it will work whatever case you use, Firefox really just needs one uppercase F... :-)
    – Arjan
    Feb 27, 2010 at 10:22
  • Indeed, I think I've been using too much Objective-C, where everything is camelCased
    – cobbal
    Feb 28, 2010 at 1:54
  • 1
    @cobbal, bad ExCuse, not EveryThing is CamelCased. ;-)
    – Arjan
    Mar 2, 2010 at 8:24

Sounds like a bug in FireFox, since the mozilla website clearly states that for opening a website (from command line) under OS-X should be:

firefox -url www.google.com

The -url can be omitted, and the -new-tab switch added to force a new tab.

  • I just tried it under windows and "firefox.exe www.google.com" opens google in a new tab, in a running browser.
    – R-D
    Feb 26, 2010 at 20:17
  • 1
    Yes, I know it should work the way you mentioned, but it doesn't for some reason.
    – viam0Zah
    Mar 1, 2010 at 14:49

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