An user script that adds Twitter button and Facebook Like button to Scratch project pages. You can use this as Chrome extension or as a greasemonkey script for Firefox.

scratch_plus.user.js

// ==UserScript==
// @title          Scratch Plus
// @description    Add Twitter button and Facebook Like button to Scratch project pages.
// @namespace      http://tsukurusha.com
// @include        http://scratch.mit.edu/projects/*
// ==/UserScript==

var pactions = document.getElementById('pactions');
var buttons = document.createElement('div');
var twitter_button = document.createElement('span');
twitter_button.innerHTML = '<iframe allowtransparency="true" frameborder="0" scrolling="no" src="http://platform.twitter.com/widgets/tweet_button.html?text=' + encodeURIComponent(document.title) + '" style="width:110px; height:21px;"></iframe>';
var facebook_like_button = document.createElement('span');
facebook_like_button.innerHTML = '<iframe src="http://www.facebook.com/plugins/like.php?app_id=235188349839830&amp;href=' + encodeURIComponent(document.location.href) + '&amp;send=false&amp;layout=button_count&amp;width=200&amp;show_faces=false&amp;action=like&amp;colorscheme=light&amp;font&amp;height=21" scrolling="no" frameborder="0" style="border:none; overflow:hidden; width:200px; height:21px;" allowTransparency="true"></iframe>';
buttons.appendChild(twitter_button);
buttons.appendChild(facebook_like_button);
pactions.appendChild(buttons);