 Firebug has been deprecated in favor of the integrated developer tools added to Firefox itself, whose functionality has been unified with those of Firebug.As Firefox 57 no longer supports XUL add-ons, Firebug is no longer compatible.Firebug 2.0 introduced many new features to the Firebug extension including JavaScript syntax highlighting, pretty print for minified JavaScript code, and a DOM Event Inspector to handle all event handlers on a web page.