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 includes a powerful JavaScript debugger that lets you pause execution at any time and have look at the state of the world. If your code is a little sluggish, use the JavaScript profiler to measure performance and find bottlenecks fast
