Firebug makes it simple to find HTML elements buried deep in the page. Once you’ve found what you’re looking for, Firebug gives you a wealth of information, and lets you edit the HTML live. Firebug’s CSS tabs tell you everything you need to know about the styles in your web pages, and if you don’t like what it’s telling you, you can make changes and see them take effect instantly. When your CSS boxes aren’t lining up correctly it can be difficult to understand why. Let Firebug be your eyes and it will measure and illustrate all the offsets, margins, borders, padding, and sizes for you.
Firebug allows you to view and manage cookies in your browser. You can deny cookies for specific sites, filter cookies, create new and delete existing cookies. You can also break into the debugger when specific cookie changes its value and see the line of script that caused the change.