how to create a keyboard shortcut in firefox for email link

I would like to create a keyboard shortcut for firefox for the EMail Link menu item. I specified shift-Command-S as the keyboard shortcut. When I hit the key sequence the File on the menubar flashes but the Email Link window never opens. Does anyone have a clue as to what I need to do to get this to work or is there a reason it doesn't work. I do use Outlook for my mail client. That shouldn't be a problem because when I manually select EMail Link from the File menu Outlook is properly used.

thanks for your help

john