I can't reproduce the event of leakage the real IP address within the initial period of establishing the first circuit.I have tried with the same settings: Firefox,Torbutton,Privoxy but now Firefox waits the necessary period till establishement of the circuit,only then,the page www.showmyip.com etc. is displayed,with the IP address of the Tor exit node.So,I am considering the hypothesis that in the two times I noticed the leakage of the real IP address,was not my IP address,but the IP address of an exit node in my country (same flag) within the range of dynamic IP addresses of my DSL provider(and I wrongly thought it was mine).Anyway,now I tested with tor-0.2.0.32(compiled from source) and Iceweasel-3.0.4.(more recent versions).When I noticed the "leakage"(perhaps it was not) I verified that the torbutton was green and privoxy was setup(as always is).
