The Mozilla source code is all publicly available and released under several different licenses. The details of Mozilla's licensing scheme aren't discussed here, but we provide information and pointers to where additional information can be found.
Several licenses are used in conjunction with the Mozilla source code, including the Mozilla Public License (MPL), Netscape Public License (NPL), GNU General Public License (GPL), and the GNU Lesser General Public License (LGPL). This wide selection of licenses was chosen to make the source available to as large a group of developers as possible.
Any code that is checked into the Mozilla source code tree needs to comply with mozilla.org's licensing policy. Because Mozilla applications can be created and stored anywhere, however, there are many different options for how to license and distribute a Mozilla-based application. One option is to sell your application with or without making all of the source available.
For more information about Mozilla's licensing scheme and the license options available to Mozilla applications, visit mozilla.org's license page at http://www.mozilla.org/MPL/. Questions about licensing issues can also be answered by posting to the license newsgroup netscape.public.mozilla.license or the license mailing list <mozilla-license@mozilla.org>.