http://zqktlwk5ilgohy63eyrptyb4mc76bunfmxcnstkmveyjnskxkpq3b5yd.onion/wiki/Web_Related_Leakage
In general, the best way to determine if a plugin/media type is obeying your proxy settings is to use Ethereal to watch network traffic. The display filter tcp.port == 80 or tcp.port == 443 can make it easier to find traffic that is bypassing Tor, though note that some media apps will use other ports and possibly even UDP.