many big company keep blocking site for their security and safety reason. this include your social networking web. u can try this alternative simple way,
just type "s" on "https://www.facebook.com" and browse. and each page u must make sure "https:" is include, or else your content will be block by your proxy.
https stands for secure connection and proxy does not block such secured connections. This is probably the simplest way to get around the proxy program as it takes little time and no one will wonder what you are up to.
bacteria comment: i only have FB account. i didnt try other. u can help me. if you success, you already a hackers now! :P