The issue is reproducible (FF3.6.3, Vista, WordPress 2.9.2 – auto-installed through the hosting provider).
The field appear to be added to the page (as evident by a, for example, page reload) – but the button doesn’t change anything on the page.
The response from admin-ajax.php is (1).
Firebug doesn’t report any issues.
PHP initial configuration values should be as follows:
magic_quotes_runtime = off;
magic_quotes_gpc = off;
register_globals = on;
via:
http://wordpress.org/support/topic/122367
