Firediff
Firediff is a Firebug extension that tracks changes to a pages DOM and CSS.
Change Tracking

Change Tracking Screenshot
Firediff implements a change monitor that records all of the changes made by firebug and the application itself to CSS and the DOM. This provides insight into the functionality of the application as well as provide a record of the changes that were required to debug and tweak the page’s display.
Snapshot
DOM Snapshot
New to version 0.2, the ability to view the exact DOM and CSS state at any given time. This allows the developer to visualize all of the changes that have been made to the page, be it the current page state or any change in between.
Dependencies
Firediff requires Firebug 1.4. The recommended version is 1.4b1 or higher.
Download
The latest release of Firediff is available here.
Contribution
For those who wish to contribute, the source code is available on googlecode within the Firebug project under the diff tree. The current release is maintained in the firediff0.2 branch. The firediff1.0 branch represents the current development branch.
Issues may be reported to the fbug issue tracker.