Firefox plugin by Adam Judson. Use Tamper Data to view and modify HTTP/HTTPS headers and post parameters, trace and time http response/requests, and security test web applications by modifying POST parameters.
Firefox plugin by Jan Dittmer. Shows the IP address of the current page in the status bar. It also allows querying custom services by IP (right mouse button) and Hostname (left mouse button), like whois, netcraft. Additionally you can copy the IP address to the clipboard. This extension was formerly ...
A Firefox plugin which allows you to view the HTTP headers of a live connection as they are sent and received.
An HTTP analyzer addon for Firefox