I also disabled any program that may be running with any ports open although I'm 100% sure there is nothing utilizing port 50000 or conflicting with it.
Here's the output in FF
Warning: Unknown property 'border-radius'. Declaration dropped.
Source File: http://localhost:50000/preview.html
Which refers to this:
border: 1px solid #8F8F8F;
--> -webkit-border-radius: 10px;
Edit: Was able to generate a couple more errors (or was more observant and discovered a couple more...
Error: console is not defined
Source File: http://localhost:50000/preview_prelude.js