The Easiest solution for saving Changes in CSS is to install the “Firebug” Addon Firediff
After you install it and you restart Firefox when you open Firebug you will find 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 Log
To Save your Changes:
Right click Inside the Change Log Area
Select “Save Snapshot“
HOW2 Getting-Started Visually with CSS Firebug Testing