What is a Source Code License?
The source code used to create an add-on is an exclusive copyright of the add-on author, unless otherwise declared in a source code license. Many add-ons on this site have open source licenses that make the source code publicly available for copy and reuse under conditions determined by the author. Most authors choose widely known open source licenses like the GPL or BSD licenses instead of making up their own. Firefox and other Mozilla software are open source.