Error Console

You can output information to console using the following method:

• Declare global variable gConsoleService:

  var gConsoleService;

• Initialize it on load:

  gConsoleService = Components.classes['@mozilla.org/consoleservice;1']
                      .getService(Components.interfaces.nsIConsoleService);

  (note, you can also use toJavaScriptConsole() function to open JavaScript console on startup)

• Define a function:

  function MyApp_logMessage(aMessage) {
    gConsoleService.logStringMessage('MyApp: ' + aMessage);
  }

• Use it like here:

  MyApp_logMessage('Initialized.');

See also: Using dump(), Using Console Service.