Firebug is free and open source; it is licensed under the BSD license. Firebug was initially written in January 2006 by Joe Hewitt, one of the original Firefox creators. The Firebug Working Group oversees the open source development and extension of Firebug. It has two major implementations: an extension (add-on) for Mozilla Firefox and a bookmarklet implementation called Firebug Lite. A cross-browser version is in development. Currently, the Firebug add-on has over 3 million active daily users.