I live in Thailand and several websites are blocked by the goverment.
Well I tried to use a proxy and checked my IP at samair.ru and the ip of the proxy is shown.
So I surf with that proxy. But the several websites are still blocked and you can see that firefox connects to the goverment site.
But it does work with chrome and internet explorer!
doesn't make any sence to me. I've deleted all cookies!
Please also try setting network.proxy.socks_remote_dns to true in about:config. You can get a list of SOCKS proxies from samair. You may have to restart Firefox and also Clear Now the Cache and Cookies in Tools (Alt + T) > Clear Recent History.
In the Location bar, type about:config and press Enter. The about:config "This might void your warranty!" warning page may appear.
Click I'll be careful, I promise!, to continue to the about:config page.