Are you sure you're opening the browser console? Ctrl + Shift + J?
var {utils:Cu, interfaces:Ci} = Components;
Components.classes["@mozilla.org/consoleservice;1"].getService(Components.interfaces.nsIConsoleService);
consoleService.logStringMessage(text);
also can try this:
var {utils:Cu, interfaces:Ci} = Components;
Cu.import('resource://gre/modules/Services.jsm');
Services.console.logStringMessage(text);
can also try this
var {utils:Cu, interfaces:Ci} = Components;
Cu.import('resource://gre/modules/Services.jsm');
Services.appShell.hiddenDOMWindow.console.log('blah');
if you're using addon sdk then instead of var {utils:Cu, interfaces:Ci} = Components;
you have to do var {Cu, Ci} = require('chrome');