Firebug Firefox Extension
Published on January 19, 2006 in FirefoxJoe Hewitt has developed a new Firefox extension called FireBug, desccribed as a “sort of a combination of the DOM Inspector and the JavaScript console, in a frame at the bottom of each browser window”. In addition, it allows you to inspect XMLHttpRequest responses and offers per-page logging. Be warned it is only an alpha release, but it worked pretty well for me in the short time I tried it.