- By running their own hostile Tor nodes
- Using zero-day vulnerability of Firefox browser
- By tracking user' browser Cookies
Finally, Don't forget to show your middle finger to FBI, NSA & GCHQ... !
This same technique is used by the Chinese government to block its citizens from reading censored internet content, and has been hypothesized as a probable NSA attack technique, but neither effort was successful enough to compromise the network as a whole.