I'm looking for clues on which tool to use to see all the resources that a browser would load when going to a particular URL. This would be similar to the list seen in Chrome's Developer Tools -> Frames, but output as something nice like JSON or XML.
You can use firebug. It is an excellent add-on. Don't forget to check the details here: http://getfirebug.com/
You want Live HTTP Headers for FireFox. As you load a website it list every URL that is loaded along with the request and response headers that are sent and received. There is a "save" button that you can use to save them all to disk.
By asking on another site, I found out that Chrome's View -> Developer -> Developer Tools -> Network panel lets you save this information by right-clicking on the bottom bit which tell you all the resources.