Mozilla Public License

Mozilla Public License
Mozilla Public License
Author Mozilla Foundation
Version 1.1
Publisher Mozilla Foundation
DFSG compatible Yes[1]
Free software Yes[2]
OSI approved Yes[3]
GPL compatible No[2]
Copyleft Limited[4]
Copyfree No[5]
Linking from code with a different license Yes

The Mozilla Public License (MPL) is a free and open source software license. Version 1.0 was developed by Mitchell Baker when she worked as a lawyer at Netscape Communications Corporation and version 1.1 at the Mozilla Foundation.[6] The MPL is characterized as a hybridization of the modified BSD license and GNU General Public License.[7]

The MPL is the license for the Mozilla Application Suite, Mozilla Firefox, Mozilla Thunderbird and other Mozilla software. The MPL has been adapted by others as a license for their software, most notably Sun Microsystems, as the Common Development and Distribution License for OpenSolaris, the open source version of the Solaris 10 operating system, and by Adobe, as the license for its Flex product line.



The license is regarded as a weak copyleft. Specifically, source code copied or changed under the MPL must stay under the MPL.[2]

The MPL was approved both as an Open Source software license by the Open Source Initiative[3] and as a Free Software license by the Free Software Foundation.[2]

History of Mozilla Public License

The Mozilla Public License (MPL) was drafted by the software company Netscape Communications in 1998 in conjunction with the Netscape Public License (NPL). The NPL was created as a means for Netscape Communications to license the source code for their browser Netscape Communicator while maintaining a certain degree of proprietary rights. They required a license that protected their source code in a manner that allowed the company to take modifications to the code made by open source developers and use that code in commercial products. That also allowed other commercial companies to build their own browsers on top of the Netscape codebase.

Much like the GNU General Public License (GPL), NPL required all modifications of original code to be released under NPL as well. However, unlike the GPL, the NPL did not require that new code which interacted with the covered code be licensed under NPL, even if the covered code was modified to work more aptly with the new code. The open source community found this provision in the NPL license allowing Netscape Communications to re-license code contributed by other users to be contrary to the goals of the free software movement.

The MPL was designed to cover new code which interacted with the covered code to be licensed under NPL. This license held even if the covered code was modified to work more aptly with the new code. The MPL does not have the same restrictions as outlined above in the NPL.

Features of the MPL

The Mozilla Public License divides the rights it grants into two sections: the rights granted by the code's initial author and the rights granted by other people who have added sections of code to the original author's work.

The rights granted by the initial author include: 1. to use, reproduce, modify, display, perform, sublicense, and distribute the source, and modified version of the source. 2. patent rights to use and make available the original code 3. to distribute works which contain the code in combination with new code, and to license the new code in any way the distributor wishes

The rights granted by subsequent users include: 1. to use, reproduce, modify, display, perform, sublicense and distribute the source of their modifications 2. patent rights to use and make available both the modifications and the entire work 3. to distribute works which contain the code in combination with new code, and to license the new code in any way the distributor wishes

There are some conditions which are attached to these rights. The most salient conditions are that all distributed copies must contain the source code, all modifications must be described in accompanying documentation, all necessary patents must be described in accompanying documentation, all copies of the code must have a statement of copyright attached, and all modified code must be distributed under MPL, although new files containing new code need not be distributed under MPL. The way in which the Mozilla Public License is drafted basically requires subsequent users to license the original code under MPL and all additional code under any kind of license. Therefore, a company can create a proprietary product from code licensed under MPL by licensing the added components in a closed source manner. The stipulation that core files stay under the MPL provides incentive for developers to improve and develop aspects of the core functionality. The MPL is GPL-incompatible because the GPL module cannot be legally linked with an MPL module. However, versions of the MPL such as MPL 1.1 have a provision that allows part of a program to offer the GNU GPL as an alternative choice, thereby allowing part of the program to have a GPL-compatible license.

Compatibility with other licenses

Unlike strong copyleft licenses, the code under the MPL may be combined with proprietary files in one program ("Larger Work"). For example, Netscape 6 and later releases were proprietary versions of the Mozilla Application Suite, by adding the proprietary AIM and other parts. The MPL treats the source code file as the boundary between MPL code and proprietary parts, meaning that a certain source file (e.g., C++, JavaScript or XUL file) is either fully MPL or fully proprietary. The GPL, in contrast, uses the process boundary of the executable as the license boundary (for details, see GPL).

Compatibility with GPL

The Free Software Foundation (FSF) considers the license a free software license, albeit one with a weak copyleft. However, "unlike the X11 license" (MIT License) the license has "some complex restrictions" making it incompatible with the GNU GPL. They urge people not to use the license because of this incompatibility unless the provision in section 13 of the MPL is exercised to provide the work under either the GPL or any other GPL-compatible license.[2]

For these reasons, the Mozilla Suite and Firefox have been relicensed under multiple licenses, including the MPL, GPL and LGPL.[8]

MPL-based licenses


  1. ^ "Mozilla Public License (MPL)". The Big DFSG-compatible Licenses. Debian Project. Retrieved 2009-06-06. 
  2. ^ a b c d e "Mozilla Public License (MPL)". Various Licenses and Comments about Them. Free Software Foundation. Retrieved 2009-06-06. 
  3. ^ a b "Open Source Licenses". Open Source Initiative. Retrieved 2009-11-06. 
  4. ^ Mozilla, MPL FAQ,
  5. ^ Copyfree Rejected Licenses
  6. ^ The Time 100: Mitchell Baker: The "Lizard Wrangler" (Marc Andreessen, Time, 18 April 2005
  7. ^ Andrew M. St. Laurent, Understanding Open Source & Free Software Licensing, pp. 62-63 (O'Reilly 2004)
  8. ^ Mozilla Relicensing FAQ
  9. ^ CePL, version 1.3
  11. ^ gSOAP Public License

External links

Wikimedia Foundation. 2010.

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