Firebug is a free, open source addon for Firefox. If you do not have Firefox, I recommend downloading it (it is also free and open source). However, other modern and standards based browsers, such as Google's Chrome, Apple's Safari, and Opera, also work well and have great built in developer tools.

Firebug, and other web development tools, makes the web development process much easier and quicker. What do I mean by this? With these tools, we can change anything on our site, on the fly, without editing or saving any files. We can type in JavaScript code with a command line interface and execute it immediately. We can view all the requests that our web page sends to servers, along with the server's reply. For example, if our map isn't able to get back map images from the server, we could examine the requests our page is making and find out if we have any typos or haven't set up our map layer properly.

Using these tools makes it a lot easier to develop not only an OpenLayers...