Awesome

GitHub Code Folding

Chrome and Firefox extension that enables code folding in GitHub

Install via the Chrome web store or Mozilla AMO

Code folding - the ability to selectively hide and display sections of a code - is an invaluable feature in many text editors and IDEs. Now, developers can utilize that same style code-folding while poring over source code on the web in GitHub. Works for any type of indentation- spaces or tabs.