Why are you clicking the desktop icon when Firefox is already open (running)? Do you want to open a new tab? You would normally click the icon (button) on the Windows Taskbar or use Alt+Tab to switch to that Firefox window. *https://developer.mozilla.org/en/Command_Line_Options ---- You can override how external links are opened via the browser.link.open_newwindow.override.external pref. The meaning of the values of browser.link.open_newwindow.override.external are the same as for browser.link.open_newwindow *1: current tab; 2:new window; 3:new tab; *http://kb.mozillazine.org/browser.link.open_newwindow (3) *http://kb.mozillazine.org/browser.link.open_newwindow.restriction (0) You can use the -no-remote command line switch to open another Firefox instance with its own profile and run multiple Firefox instances simultaneously. *http://kb.mozillazine.org/Opening_a_new_instance_of_Firefox_with_another_profile *http://kb.mozillazine.org/Using_multiple_profiles_-_Firefox