As mentioned above, Firebug is a very important addition to the web developer's toolkit, but it is one that not many people will have used. Most of the other tools are fairly intuitive to use at a basic level, but Firebug needs a slight introduction.
The first and most important feature of Firebug is the Inspect Element feature. This feature can be accessed by right-clicking on any HTML element on the page and selecting Inspect Element from the context menu.
Let's visit the Packt Publishing homepage (http://www.packtpub.com) and try it out.
When we click the Inspect Element menu item, a new area should appear at the bottom of our page the looks like the next screenshot. The area that appears will usually be broken into two panes, our HTML structure on the left, and CSS information on the right. The item we selected with our right-click will be highlighted in blue, and the CSS styles applied to it will appear in the right pane.
Some of the CSS styles...