Reading an article about WSGI, I ran across an excellent tool for HTTP exploration:
It is very useful to be able to see the HTTP information being sent back and forth between a web browser and a server. One good tool for doing this is the LiveHTTPHeaders extension for the Firefox web browser which, when loaded, is visible in the sidebar and displays the HTTP information sent and received on each request. Once it’s installed, you can select View->Sidebar->LiveHTTPHeaders from the menu to load the extension in the sidebar.
Click on the link above to download and install. It’s really well done.