Activity window for Firefox?

One of the features in Safari for OS X that keeps me loyal -- along with bookmark syncing -- has been the Activity window. If you haven't noticed it before, you can open it under Window>Activity in the top menu bar, and it will trace every piece of content that is called by a document. You can then double-click on any of the line items in the Activity window to load that specific file. As a Flash developer, this has helped me out countless times when debugging a movie (why isn't my damn XML file loading?), as well as with javascript and just about anything else.

I'm looking for something similar for Firefox but haven't found anything yet. If anyone reading this knows of an extension that replicates this, drop me a line and I'll post it here.

Update: Several people have chimed in that you can simply right-click on a page and select "Page Info." True, but the dialog only shows content that was initially loaded -- not subsequently. In Safari for example, when a Flash movie changes states and retrieves a file, the Activity window updates with an absolute path to the file. Also unlike Page Info, you can leave Activity open while surfing other sites, and it will show all activity for additional pages as well. I'm hoping for a Firefox extension I can simply leave open, and refer to if need be.

Update: It's been found: LiveHTTPHeaders. Not as elegant as Safari, but it does offer live updating of all requested assets. Select the "Generator" tab in the extension, and check all the "Show" options on the right. It'll display everything that's going on. Thanks to everyone that suggested this.