NOTE: Firefox and Chrome do not allow access to some local filesystem files used in testing. So, if you're opening this through a file:// URL, you should instead go through a web server : either through a local one (http://localhost/...) or through a remote one (but you need SSL : https://webserver/...).
Another option is to force your browser to accept that (but you'll open a security breach) : on Chrome, you can start it with --allow-file-access-from-files command-line argument; on Firefox, you can set privacy.file_unique_origin to false in about:config