I have created a web page. Now, should I align that DIV to the left? Or should it be centered? Will it look good if the font size is 11px or 12 px? should I change the background color to yellow or magenta? Now again, what was the class selector that I used on that DIV? How much should I specify the left value as for this element, to align it with the rest?
Imagine wanting to do all that and more... You update your web page on the server. Refresh! Tweak the page on the server! Refresh! Tweak again! Refresh!
Enter Firebug. Firebug is a mozilla addon that helps ease a web developer's life. It allows you to inspect the html elements on a page; edit and modify them; run remote scripts; see the network utilisation; view the various requests that your page makes; view each request's query and response; inspect the DOM; inspect the layout of the page; and the list goes on and on.
For someone looking to architect the web, firebug is a must-have.