A while back, someone tipped my off to the Activity Window in Safari. This window is fantastic if you doing Flash development and need to debug on a live website. It will show you any images, videos, XML files, or anything else that’s getting loaded into your page.

I’m a Firefox user, so I went looking for an add-on that would do the same thing in Firefox. While it’s not quite as organized (i.e., it isn’t structured in a tree menu like the Activity Window), the “generate” tab of livehttpheaders is a pretty close substitution.

Originally found on What Do I Know.

UPDATE:  As Tim notes below, Firebug also has this capability. It’s under the ‘net’ section of the Firebug window. You have to choose to enable this feature before you see anything.