Edit, debug, and monitor CSS, HTML, and JavaScript live in any web page

Firebug is a add-on for Mozilla Firefox that integrates with Firefox to put a wealth of development tools at your fingertips while you browse.
You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.
You can prank your friends by showing them an edited website.
Firebug is free and open source (BSD)

Inspect and edit HTML

Tweak CSS to perfection

Visualize CSS metrics

Monitor network activity

Debug and profile JavaScript

Quickly find errors

Explore the DOM

Execute JavaScript on the fly

Logging for JavaScript

For other browsers you can drag and drop this bookmarklet and whenever you will click it, Firebug will open in the webpage.

DOWNLOAD HOMEPAGE BLOG