by Joshua Johnston.
Hi Paul,
I'm not familiar with the XML-RPC implementation in Moodle but usually you cannot make a browser request to an XML-RPC server because it expects the request body to contain XML with the name of the remote function to call.
For testing purposes, enable the rest protocol and then try with the url:
http://<my-moodle-site>/webservice/rest/server.php?wstoken=<token>&wsfunction=core_course_get_courses
Note: The REST protocol isn't real REST, it is a roll-your-own type protocol with a single endpoint that switches method based off query string parameters