<script type="text/javascript">
var _console = window.console;
Object.defineProperty(window, 'console', {
set: function (x) {
if (x.exception) { // check if this is actually Firebug, and not the built-in console
alert('Firebug on');
}
_console = x;
},
get: function () {
return _console;
}
});
</script>
Fuente: Googleando...
::http://stackoverflow.com/questions/3745140/detect-firebug-opening-and-closing
Saludos