This works by calling a SOAP service.. View the source of this page for details on how it was called. If you compile mozilla DEBUG, the message sent and received will be logged to the console This loads js files soapisprimeproxy.js which relies on soapproxy.js, which implement a SOAP proxy on top of the low level SOAP API in Mozilla. In a future version of Mozilla, it should be possible to construct SOAP proxies directly from the wsdl file.
Since this service is friendly to untrusted applets, it may be called without requesting additional privileges from the user.
Other services are available on the X Methods Website. Experimenters may wish to create other tests which exercize services, with specific user interfaces.