"The MPL has been approved as both a free software license (albeit one with a weak copyleft) by the Free Software Foundation and an open-source software license by the Open Source Initiative. The MPL allows covered source code to be mixed with other files under a different, even proprietary license. However, code files licensed under the MPL must remain under the MPL and freely available in source form. This makes the MPL a compromise between the MIT or BSD licenses, which permit all derived works to be relicensed as proprietary, and the GPL, which requires the whole of a derived work, even new components, to remain under the GPL. By allowing proprietary modules in derived projects while requiring core files to remain open source, the MPL is designed to motivate both businesses and the open-source community to help develop core software." - http://en.wikipedia.org/wiki/Mozilla_Public_License
"The MPL has been approved as both a free software license (albeit one with a weak copyleft) by the Free Software Foundation and an open-source software license by the Open Source Initiative. The MPL allows covered source code to be mixed with other files under a different, even proprietary license. However, code files licensed under the MPL must remain under the MPL and freely available in source form. This makes the MPL a compromise between the MIT or BSD licenses, which permit all derived works to be relicensed as proprietary, and the GPL, which requires the whole of a derived work, even new components, to remain under the GPL. By allowing proprietary modules in derived projects while requiring core files to remain open source, the MPL is designed to motivate both businesses and the open-source community to help develop core software." - http://en.wikipedia.org/wiki/Mozilla_Public_License