If you ever wanted to see the data that is being sent from yoru browser to a web server or wanted to the response coming back from the server, you previously needed to resort to proxy techniques like burpproxy, listed on an interface via tcpdump or use one of the commercial traffic analysis applications.
Thanks to Adam Judson you can now do this all from the comfort of your Firefox browser using his Tamper Data extension. Tamper Data installs a new sidebar that allows you to enable/disable “tampering”. When in tamper mode, you can intercept all requests and potentially modify them before they are being sent to the receiving web server.
Highly useful if you need to debug the traffic from/to your web application directly from within your browser.
Great job, Adam!