What is the best free css tool I can use, preferably an extension to firefox, chrome or IE? I would like to hover my mouse or click on parts of the webpage and it tell me where exactly the color is being set, where the margins are actually set in the css file, etc.... Thanks!
Both Firefox & Chrome ship with Development tools like you're requesting.
Press CMD / CTL + SHIFT + I in either browser or right click to Inspect Element
The left panel in both is the DOM structure, the right panel is CSS.
Hovering elements in the level panel will show padding (green) and margin (red)
You can also change CSS values in the right panel and see the results live.
Read about Chrome Dev Tools
Read about Firefox Dev Tools