Trouble with part 3 of Direct Uploads to S3

I am working through your Direct Uploads to S3 series and have run into a snag that I am hoping you can help with.

Everything has worked as advertised UNTIL I added the js in episode 3. Now I am getting the following error which I understand to be a defence against cross site scripting.

XMLHttpRequest cannot load https://triggerchicago.s3.amazonaws.com/. Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'https://rails-tutorial-stallarida.c9users.io' is therefore not allowed access. The response had HTTP status code 403.

I have found a bunch of hacks to get it working but all seem to be questionable from a security standpoint. How did you get around this in your demo? I am hitting S3 from Cloud9 IDE.