Mozilla as a Debugging Tool

How do you debug web applications?

Passing requests through a proxy is one of the most convenient and powerful ways to debug an application during development. First you try cfdump, cflog, some debug output in the browser, and maybe some JavaScript alerts. If you are using a Flash front-end, you might use trace() or the NetConnection Debugger. But there is nothing like passing requests and responses through a proxy to give you the entire picture.

I have used a lot of different kinds of proxies to find out exactly what was occurring between the client and the server. I have used command-line proxies that log to a file, Java based proxies that I wrote myself, and graphical tools with all kinds of features. It never occurred to me, however, that one could simply be built right into a browser. Or, more accurately, if your browser could expose entire HTTP requests and responses rather than just HTML source, you don’t even need a proxy. If you can view the raw headers of an email message in most email clients, why not be able to watch HTTP headers in your browser? Well, if you use Mozilla, now you can:

http://livehttpheaders.mozdev.org/