Legal Definitions - MPL

MPL stands for Mozilla Public License.

The Mozilla Public License (MPL) is a type of open-source software license developed by the Mozilla Foundation. It permits users to freely use, modify, and distribute software code. A key characteristic of the MPL is its "weak copyleft" provision. This means that if someone modifies software released under the MPL and then distributes that modified version, they must make their changes publicly available under the same MPL terms. However, unlike "stronger" copyleft licenses, the MPL generally allows MPL-licensed code to be combined with other proprietary or open-source code in a larger project without requiring the entire larger project to also be released under the MPL. It primarily focuses on ensuring that modifications to the original MPL-licensed files remain open.

• Example 1: Developing a Browser Component

  A software company is building a new web browser and decides to release its core rendering engine under the MPL. This allows other developers and companies to freely use, study, and improve the engine. If another company takes this engine, modifies its code to add new features, and then distributes their modified engine, they are legally required to make those specific modifications public under the MPL. However, the original company can still develop proprietary user interfaces or additional features for their browser that are not MPL-licensed, as long as those parts don't directly modify the core engine's MPL-licensed code.

  This example illustrates how the MPL promotes collaboration on a specific component (the rendering engine) by ensuring modifications to that component remain open, while still allowing for proprietary elements in the broader product.

• Example 2: Contributing to an Open-Source Project

  An independent developer creates an innovative new plugin for an existing open-source email client that is licensed under the MPL. When the developer submits their plugin code to be integrated into the main project, they agree to license their contribution under the MPL. This ensures that their new feature, once part of the email client, adheres to the project's existing licensing terms, maintaining the open-source nature and allowing for future community development and modification of the plugin under the same conditions.

  Here, the MPL ensures that contributions to an existing project align with its open-source principles, keeping all parts of the software freely modifiable and distributable under consistent terms.

• Example 3: Integrating into Proprietary Software

  A large financial institution wants to use a highly efficient data encryption library, which is licensed under the MPL, within its proprietary internal banking software. The institution can incorporate this library into their system without being forced to open-source their entire banking application. However, if their in-house developers make any improvements or bug fixes directly to the encryption library's code, they are obligated to release those specific modifications back to the public under the MPL. This allows the institution to benefit from the open-source library while contributing back any improvements to its core.

  This demonstrates the "weak copyleft" aspect of the MPL: a company can use MPL-licensed code within a larger proprietary system, but any changes made to the MPL-component itself must be shared back with the open-source community.