Firebug 1.5,  not new to anyone here. It’s one of the most popular developer tool to debug , track network activity and tweak JavaScript, CSS, HTML and DOM of any website. I have personally used Firebug to find errors in my web projects and it works wonders. You can read a complete step-by-step review of this spectacular tool (Firebug Demystified – Link).

The newly updated Firebug has improved add-on stability and other new advancements have been introduced. Most of all, it has been made compatible with the new Firefox 3.6 browser. Among the updates in Firebug 1.5 are a much-improved Inspector tool, which allows you to select any element on the page and see the HTML and any applied CSS rules; and several major new features for the Net panel, which can debug XMLHttpRequests. [More features - Firebug Wiki ].

Download Firebug 1.5 – Link