I have small ajax problem related to cross domain as i see it.
On localmachine i created html example with some ajax: in registration text field user types \'username\',
The 200 status reported in Firebug does not indicate the validity of the cross-domain ajax call, be it successful or not.
You might want to try using a proxy method to perform the call.
E.g. JavaScript: Use a Web Proxy for Cross-Domain XMLHttpRequest Calls