FireBug

FireBug Description

BSEditor: FireBug lets you explore the far corners of the DOM by keyboard or mouse. All of the tools you need to poke, prod, and monitor your JavaScript, CSS, HTML and Ajax are brought together into one seamless experience, including a debugger, error console, command line, and a variety of fun inspectors.
Some Fun Features
Logging for web pages

Web developers have suffered with "alert debugging" for centuries. If you enjoy clicking the "Ok" button 40,000 times a day, FireBug is not for you. Otherwise, you'll enjoy having the ability to log messages from JavaScript in your web page directly to the FireBug console.
JavaScript Debugging

Want to stop your JavaScript and step through it line by line? No need to fire up a big fat debugger. FireBug includes a simple lightweight way to set breakpoints in your Scripts and examine every step of execution.
Errors at your Fingertips

Nobody likes to see errors in their web pages, but with FireBug you won't mind as much. FireBug adds a little icon to the Firefox status bar which tells you if your page is busted. Open up the FireBug panel and you're looking at the errors that occurred in that page, and only that page. No more digging through the muddy pile of errors in the JavaScript Console window.
Inspectors galore

Elements and styles and Events, oh my. There's a lot going on behind the curtain of a web page. FireBug's inspectors let you stroll lazily through the DOM using the familiar hyperlink model of the web. If you see an object reference, you can click it to inspect it.
Command line

If you enjoy "alert debugging" then you probably also enjoy typing "javascript: " urls in the location bar all day. If not, then you'll enjoy using FireBug's Javascript Command line instead.
Ajax Request Spy

If you feel hip every time you fire off an XMLHttpRequest on your Ajax website, FireBug will secure your place amongst the avante garde. �.You can free download FireBug from Brothersoft now.