Bypassing at school

Ok so i installed firefox onto my memory stick, and i can load it up at school, and surf the internet, but still get the blocked sites, but as i dont use the schools browser i can change the options, by going file>Optitions>Advanced>settings (this is if your using the newest vertion) from there i can change aload of settings. Now my school is set to Manual proxy configuration and all the proxys are set to: proxy.embc.org.uk port: 80, now i dont know but, is this anything to do with blocking the sites, and if it is, can i change it to somthing else so it dosnt?
Thanks
Nick :)