Run both Firefox and Google Chrome, both have their merits and features not available on both browsers.
Run the developer tools and/or firebug debugging utility.
Activate the developer utility to view the HTML and CSS related to a given element.
With these tools it is also possible to modify html and/or css on the fly and observe changes.
This is a great way to observe simple changes in CSS settings, such as color, size, margin, padding, and so on.
On Google Chrome install the CSSViewer utility.