That's not accurate. The Firefox zero-day wasn't part of compromising Freedom Hosting, just users of sites that it hosted. As I understand it, Freedom Hosting itself was compromised through pwning the server from a guest site under FBI control. Also, the FBI didn't just use a "tracking cookie" against users. They dropped a Windows executable that phoned home.
All the more reason Tor users should implement a default-deny security policy, unless you trust your AVs to detect these.
They probably would get more usefull results by implanting tracking chips in all camels in the Middle East. Camels are an excellent means of carrying whispered secret information. http://i.ytimg.com/vi/vd_PZkkhByk/0.jpg