Anonymous proxy Browser
With the help of different testsites you can tell whether your browser has been configured right. For JonDonym and Tor Onion Router we recommend specifically the JonDonym Anonymity Test
IP address check
The anonymity test will check your IP address in many ways. If the configuration was correct your real IP address will be hidden. But time by time there are configuration misstakes or bugs in your browser and deanonymisation is possible. Check the displayed IP address. If it is red you are surfing on the Net without any protection by JonDo or Tor.
Make sure that your browser cannot run ActiveX, Java and Flash without your prior confirmation. An automatic execution of these plugins will usually give away your IP address and important system settings, and can thus revoke anonymity completely or at least partially with respect to that website. You can use a proxifier like ProxyCap or Widecap to avoid these issues.
IP address leak by Flash player.
The anonymity test will give you a quick overview about HTTP header informations send by your browser to websites. These informations can used to calculate an individual fingerprint of your browser. The EFF setup a demonstration project Panopticlick. All fields should be colored green or colorless. Orange is usually tolerable, red can be devastating to your anonymity.