Hi Phil,
I assume that you launch the generated WebGL/Javascript application directly within a browser on your PC.
If your browser allows the access to local files, you can directly open the generated HTML page with the browser. Otherwise, if access to local files is not allowed for security reasons, please copy all files to a web server. Alternatively, you can use a local web server, e.g. HFS - HTTP File Server.
See also Getting started with JavaScript/WebGL (Installation Step 2).
Does this solve the issue?
Best regards,
Manfred-