The Firebug extension for Firefox by Joe Hewitt just rocks. It is the culmination of a few different Firefox extensions: the Web Developer Tool Bar, the Dom Inspector, Viewed Rendered Source, and Venkmen (the Javascript debugger). Firebug borrows from these extensions and more, packages them up in a nice, tasty usable extension.

It has a Javascript debugger that lets you set arbitrary breakpoints; DOM inspector that not only lets you see the structure of your page, but also any styles and events on each node in the DOM tree; an AJAX console viewer so you can see the raw HTTP requests and responses; and a console, where you can see Javascript and CSS errors and type in arbitrary Javascript.

The inspector alone is worth the price of admission, it allows you to hover over elements on a page, and it will not only highlight the element on page, but also highlight the corresponding element in the rendered source, and show you not only the styles applied to it, but where it got those style rules from. This is probably the feature of firebug that I use the most, and it has made my job as a web developer infinitely easier.

It provides a host of great Javascript functions as well through a console object. Not only can you send it debug, info, warning, and error log messages (no more alert debugging, horray!) but you can send it assertions—great for design by contract.

I have noticed a few problems with it. Every once in a blue moon my browser seems to crash, which might be a fault of firebug. It really is a once-in-awhile issue, like 2-3 times a week after a period of heavy usage. Firebug also has some known issues with regards to viewing HTTP Requests and Responses. Synchronous requests cause it to fail, as well as documents that are XML (like XHTML, for instance). In actual fact, these are Firefox issues, and not Firebug issues, but there is a good chance these issues are being worked on.

Despite these problems, Firebug is a very usable, very cool extension. If you do any kind of web development, as a job, or as a hobby, it is well worth installing.

Techno Chocolate! (oon tsch oon tsch oon tsch... dooo do do do do do!)