Another solution that may work well, download Tor with Vidalia, when you install it you can install a Tor button in Firefox, which allows you to use Firefox through the Tor proxy. The only thing to keep in mind is most of the Tor proxies seem to be in Germany, so when you open web pages you'll have to change the language to English, or whatever your language of choice is, which would be somewhere on the web page.
I say Tor because it's a GREAT proxy, and it very purpose is to provide Internet freedom to countries like China, Iran, etc., it changes your proxy IP every couple minutes, it's a really good service, and really easy to use.
One thing to keep in mind, with the latest versions of Ubuntu it seems that when you start Vidalia it will say it fails to connect to the Tor network, but it's because Ubuntu seems to start Tor on system start when it's installed, so if Vidalia says it can not connect, this is probably why, in which case you will not even need to start Vidalia, just start Firefox and make sure the Tor button is ON so that you connect through the proxy. If Vidalia says it successfully connects to the Tor network, then that means your Ubuntu is not making it start automatically, and you will need to start Vidalia every time you use it.
I hope this helps, and I hope it's not too confusing.