Many GitHub repositories doesn't use GitHub Pages to host their HTML files. GitHub HTML Preview
allows you to render those files without cloning or downloading whole repositories.

If you try to open raw versions of any HTML, CSS or JS files in a web browser directly from GitHub,
all you will see are sources. GitHub forces them to use the "text/plain" content-type. This script
overrides it by using Yahoo! Query Language.

To use it, just prepend this to the URL of any HTML file: http://htmlpreview.github.com/?

E.g.: http://htmlpreview.github.com/?https://github.com/twitter/bootstrap/blob/master/docs/index.html

GitHub HTML Preview is tested under Google Chrome and Mozilla Firefox, and it should work with any
websites, not only GitHub.