Some admin (for good of course) uses Squid’s setting to block bad sites. But sometimes, the good ones also got blocked. Actually, to prevent good sites blocked, there’s also a good-site-list. Thanks to firefox developer and greasemonkey extension developer, we could do some tricks. I try to do a simple hack which rely on the good-site-list. The idea is to rewrite any URL with an extra fake parameter, one of the good site, which very likely added by the administrator to the good list. Well, use the script at your own risk, you’re responsible for whatever you do with that script. Happy Browsing!
(hint: try to access a blocked site with added '?google.com' on the URL or '&google.com' if the original URL already has a '?' on it. If it's working, this hack is for you)