On Firebug if you want to Save HTML and CSS Changes your can Use the “Firebug” Addon Firediff
After you install it you will find on Firediff Window a New Tab Changes that will serve to Inspect and Save changes made on your CSS file.
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To Inspect the Changes you made:
Changes > Change LogTo Save your Changes:
Right click Inside the Change Log Area
Select “Save Snapshot“
In a Similar Way you can Save also the HTML Changes made when Editing…
HOW2 Getting-Started Visually with Firebug CSS Testing
Good Development with Firebug! :)