From the short readme that comes up when we start a new node.js project:
"Once the server is running, open the project in the shape of 'https://projectname-username.c9.io/’."
I think the naive user might actually use a hyphen as shown, whereas it’s a dot that works. Also, c9 gets redirected to c9users and at least in my case, filing a security exception in the browser, after getting a warning about miss-configured website, was required. In short, I think the readme needs revision.