http://bl.ocks.org is a simple Gist viewer for HTML/JavaScript examples.
To install the Safari extension, download bl.ocks.safariextz and then double-click.
To install the Chrome extension, download bl.ocks.chrome.crx. Then, go to chrome://extensions and drag the downloaded file onto the list of extensions.
To install the Firefox extension, download bl.ocks.firefox.xpi. Then, select Add-Ons in the Tools menu, click on the Extensions tab, and drag the downloaded file onto the list of extensions.