One of the most user-friendly features of Firefox is its low-keyed presence. Firebug opens in a separate window or it will appear at the bottom of your browser. It will also provide fine grain control over the site that is being enabled. Firebug specializes in locating HTML elements buried deep down in the page. Once the the element is found, Firebug disseminates a flow of information while giving the developer the opportunity to edit the HTML live.
One of Firebug's most popular web tools is its ability to use the CSS tabs to tell you everything you need to know about a web page styles. The developer has the option of making instant changes to the page. Additionally, it detects when your CSS boxes aren’t lining up properly. It automatically measures and illustrates offsets, margins, boarders, padding and sizes.