High Quality Content by WIKIPEDIA articles! Firebug is a web development tool that facilitates the debugging, editing, and monitoring of any website`s CSS, HTML, DOM, XHR, and JavaScript; it also provides other web development tools. Firebug`s JavaScript panel can log errors, profile function calls, and enable the developer to run arbitrary JavaScript. Its net panel can monitor URLs that the browser requests, such as external CSS, JavaScript, and image files. The net panel can display both request headers and response headers for each page asset; it can also estimate the time each asset took to load.