I am just testing the new ajax debug toolbar and my request are not visible in the profiler.
It works if the url are relatives and not absolute.
"http://localhost/sf_test/app_dev.php/demo/test" is not handled, but "/sf_test/app_dev.php/demo/test" works.

That seems normal regarding this code:

/* prevent logging AJAX calls to static and inline files, like templates */
if (url.substr(0, 1) === '/' && !url.match(new RegExp("{{ excluded_ajax_paths }}"))) {

https://github.com/symfony/symfony/blob/master/src/Symfony/Bundle/WebProfilerBundle/Resources/views/Profiler/base_js.html.twig#L181

excluded path does not work also:
"http://localhost/sf_test/app_dev.php/_wdt" does not match regexp "^/_wdt".

Did I miss something ?

tested on Firefox and Chrome (Ubuntu)