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Add-on for FireFox 5 (or newer)
Version: 1.1.1.10
Download from addons.mozilla.org

Extension for Internet Explorer 6 (or newer)
Version: 1.1.0.2
Download for Windows XP/Vista/7 . Size: 235 KByte.

Also you can download extension for Google Chrome from Google from Chrome Web Store.

Source code: http://code.google.com/p/social-network-tools/source/browse/.