The application form is [https://docs.google.com/a/mozilla.com/forms/d/1Pa5IsuhT6vMUfg0HUXxr7SzrSwq5fpiZfZIJVPxN1Mc/viewform here]. Applications are accepted on an ongoing basis.
If you are looking for a good example, you can read a successful application: [https://wiki.mozilla.org/images/b/b7/Django-application.odt Django].