ExpandCollapseAllDiffsInGithubDiffPage.js

// in chrome console
// if many diffs will be slow :P 

var clickAction = function(element) { element.click(); }

var elementsExpand = document.getElementsByClassName('load-diff-button');
Array.prototype.forEach.call(elementsExpand, clickAction);

var elementsCollapse = document.getElementsByClassName('btn-octicon');
Array.prototype.forEach.call(elementsCollapse, clickAction);