Mozilla licensing is the set of licences and policies under which Mozilla publishes its software, most prominently the Firefox web browser and the Thunderbird email client. Mozilla states that all of its software is open source and free software, available at no charge with access to the source code, which may be modified and redistributed subject to certain restrictions.[3] The principal licence is the Mozilla Public License version 2.0 (MPL 2.0), which Mozilla also maintains for other projects as its custodian.[4] Executable builds of Firefox and Thunderbird are made available under the MPL, and Mozilla states that there is no separate end-user licence agreement.[3][11] Trademarks are handled differently: Mozilla describes strict enforcement of its names and logos, which the code licence does not cover.[3]
For software asset management (SAM), Mozilla software has no licence metric. Nothing is counted per user, device or core, and no licence key or activation is involved. The compliance questions arise when an organization distributes Mozilla code or binaries to third parties, embeds MPL components in its own products, or uses Mozilla trademarks. The sections below follow the House rules template. Mozilla has no commercial editions, and the metric and virtualization sections say so.
Licences and versions
Mozilla Public License 2.0
MPL 2.0 is the current version of the licence.[4] SPDX records it as released in January 2012,[9] and the Open Source Initiative (OSI) lists it as approved on January 9, 2012, with the Mozilla Foundation as licence steward.[7] The SPDX License List (version 3.29.0, 2026-09-16) marks MPL-2.0 as both FSF Free/Libre and OSI Approved.[8] Mozilla’s FAQ describes the MPL as “a simple copyleft license” whose copyleft is file-level: modifications to MPL files must be shared, but MPL code may be combined with code under other licences, open or proprietary.[2] The obligations are summarised below and covered in detail in Mozilla Public License 2.0.
MPL 2.0 comes in two variants, set by the notice the original author attaches. With the standard Exhibit A notice, MPL code may also be distributed under the GNU GPL, LGPL or AGPL when combined with works under those licences. If the author also attaches the Exhibit B notice, the code is “Incompatible With Secondary Licenses” and this option is removed.[1] SPDX uses the identifier MPL-2.0 for the first case and MPL-2.0-no-copyleft-exception for the second.[9]
Earlier licences
Mozilla source code was first released under the Netscape Public License 1.0. MPL 1.0 and MPL 1.1 followed, and between 2001 and 2004 Mozilla moved its code base from MPL- or NPL-only terms to an MPL/GPL/LGPL tri-licence. Mozilla now describes NPL 1.0, NPL 1.1 and MPL 1.0 as obsolete. It describes MPL 1.1 as obsoleted by MPL 2.0 and not recommended for new code.[5] MPL 2.0 was drafted over 21 months in a public process. Its main changes from MPL 1.1 are simpler notices, patent terms closer to those of the Apache License, and compatibility with the Apache License and the GPL.[6] Code received under MPL 1.1 may be distributed under MPL 2.0, because both versions allow later versions to be used (rule).[1][6]
Licences inside Mozilla repositories
Mozilla’s Source Code License Policy (version 4.1) requires modifications to existing product code to stay under MPL 2. New Mozilla projects may choose MPL 2.0 or the Apache License 2.0, and trivial code such as test cases is dedicated to the public domain under CC0.[10] Third-party code in product code must be under the MPL or a compatible licence. The policy lists CC0 and other public domain dedications, MIT, New BSD and similar permissive licences, Apache 2.0, and GPL/MPL dual licences as compatible. It lists CC-BY and the GPL as incompatible.[10] Mozilla websites use Creative Commons licences for their text, a separate regime from the software.[3]
Editions
Mozilla sells no commercial editions of Firefox or Thunderbird. The licensing differences that matter are between release channels, not editions. Firefox is offered as the Firefox release channel and as Firefox Extended Support Release (ESR). From Firefox 155 (September 2026) the release channel ships a new major version every two weeks, and ESR ships one new major version a year, which then receives security updates.[19] Thunderbird desktop offers Release, Extended Support Release, Beta and Daily channels.[22] All channels are under the same licence terms. See Firefox ESR and enterprise deployment.
Thunderbird is developed by MZLA Technologies Corporation, a wholly owned for-profit subsidiary of Mozilla. The project describes Thunderbird as free and open-source software under MPL 2.0.[21]
Metrics
There are no Mozilla licence metrics. The MPL grants a royalty-free licence to use, reproduce, modify and distribute (rule).[1] The MPL FAQ states that using MPL software requires nothing, and that the MPL creates obligations only when software is distributed outside the organization. Modification and distribution inside a company count as private (rule).[2] The one metered offering is the optional Thundermail hosted subscription, sold at a published plan price rather than per licence (see Programs).[23]
Counting / floors
No counting, floors or minimums apply to Firefox or Thunderbird. The Firefox Terms of Use (effective 2026-09-16) grant a personal, non-exclusive licence to install and use the Executable Code version of Firefox from an authorized source, and they do not apply to the source code. The source code remains under open source licences, including the MPL, which allow use, copying, modification and distribution subject to those licences and the Trademark Guidelines (rule).[12] The Terms also cover optional services such as sync, which require a Mozilla account and separate terms.[12]
Obligations when distributing or modifying
MPL obligations apply only when Covered Software is distributed outside the organization. The main ones are:
| Situation | Obligation | Source |
|---|---|---|
| Distributing binaries (installers, embedded builds, minified JavaScript) | Make the MPL source available and tell recipients how to get it, at no more than the cost of distribution (rule) | MPL 2.0 §3.2(a)[1] |
| Distributing source, including changes | Keep it under the MPL and tell recipients where the licence is (rule) | MPL 2.0 §3.1[1] |
| Keeping notices | Do not remove licence, copyright, patent or warranty notices in the source (rule) | MPL 2.0 §3.4[1] |
| Combining with proprietary code | Only the MPL files and changes to them are copyleft. The Larger Work may use any licence (rule) | MPL 2.0 §3.3; FAQ Q11[1][2] |
| Licensing your binaries | You may sublicense the executable under your own terms if they do not restrict source rights (rule) | MPL 2.0 §3.2(b)[1] |
| Selling support or warranty | Offer it only on your own behalf (rule) | MPL 2.0 §3.5[1] |
The FAQ states that Mozilla-provided Firefox executables already meet the Section 3 notice requirements. A business that passes unchanged Mozilla builds to others therefore has no further MPL obligations, although the trademark-based Distribution Policy still applies (see below).[2]
Virtualization & partitioning
Not applicable. The MPL and the Firefox Terms of Use set no limits or counting rules for virtual machines, containers, VDI or terminal servers, and Mozilla publishes no partitioning policy.[1][12]
Cloud / BYOL
There is no bring-your-own-licence mechanism, because no licence is purchased. The MPL FAQ explains that code running only on a server is not “distributed”, while HTML, CSS and JavaScript sent to the client are (rule).[2] Hosted services that give users remote access to Firefox are subject to the Trademark Guidelines. Such a service may not carry a Mozilla trademark in its name, but it may say in words that it features unaltered Firefox (rule).[13]
Trademarks and redistribution
MPL 2.0 Section 2.3 grants no rights in Contributors’ trademarks (rule).[1] Firefox, Thunderbird, Mozilla and other names and logos appear on Mozilla’s trademarks list, which gives sample notices attributing the marks to the Mozilla Foundation.[25] Under the Distribution Policy, unaltered copies of Firefox from Mozilla.org may be redistributed without permission. The distribution must be free of charge, must not collect personal information, and must use the latest version with no added extensions, changed defaults or modified installer (rule).[14] A modified build may not keep Mozilla trademarks without prior written consent, typically under a distribution agreement (rule).[14] Projects built on Mozilla code must choose their own branding, and may state in words that they are based on Mozilla technology if they add a statement of non-affiliation.[13] See Mozilla trademark and distribution policy.
Bundled third-party components
Mozilla binaries are not entirely MPL code. The about:license page generated from the Firefox source tree states that most code is under MPL 2.0 and the rest under various other free and open source licences. It reproduces the licences whose text must accompany distributions (rule).[16] Under its binary components policy, Mozilla may add operating-system vendor code under non-MPL licences to installers for proprietary platforms, and it discloses that code in about:license.[15] On Windows, the about:license template carries the Microsoft Distributable Code terms for the C and C++ runtime libraries, which may be used and distributed only as part of the product (rule).[16] The Firefox Terms of Use add that Firefox may download third-party content decryption modules for some video, and that these may not be open source.[12] Organizations that redistribute or rebuild Firefox inherit these third-party notice obligations.
Programs
Mozilla’s paid offerings sell services, not rights to use the software.
- Firefox Professional Support offers private issue triage and escalation, defined response times, custom development and collaboration with Mozilla engineering. Organizations request it through an inquiry form, and the Firefox for enterprise page describes it as in early access. No price is published.[17][18]
- The Unaltered Software Distribution Policy and a written distribution agreement are the two routes for redistributing Mozilla-branded software.[14]
- The Thundermail subscription bundles hosted email, Appointment and Send. Its Early Bird Plan is listed at USD 6 per month, paid annually, and the service is in beta with a waitlist.[23] Thunderbird says it runs as a for-profit subsidiary so that it can offer optional paid services.[21]
SAM practice
The following practice notes are commentary drawn from the cited documents.
- Discovery. Firefox and Thunderbird are commonly installed per user or per machine, and Windows MSI installers exist for both.[24][22] Inventory should record the product, channel (release or ESR) and version, because channel determines the support lifecycle.[19]
- Version and end-of-life tracking. Mozilla publishes ESR end-of-life dates on its release calendar. As published on 2026-09-27, ESR 140 reaches end of life on 2026-10-13 and moves to ESR 153. ESR 115 is supported only on Windows 7 to 8.1 and macOS 10.12 to 10.14, up to March 2027 (rule).[20] An unsupported version is a security and lifecycle issue, not a licence shortfall.
- Internal use against redistribution. Internal deployment has no licence position to reconcile.[2] Review is needed where the organization ships software that contains MPL files, rebuilds or rebrands Firefox, bundles Firefox with devices or products, or offers Firefox as a hosted service. Those cases trigger source-availability, notice and trademark obligations.[1][14]
- Licence identification. MPL-2.0 and MPL-2.0-no-copyleft-exception carry different GPL compatibility, so component inventories should record the Exhibit B marking.[9]
Mozilla describes its licensing overview page as informative, not authoritative. Anyone reusing or redistributing Mozilla material should check the licensing in the item itself, such as a file header or the software’s About box, which takes precedence where the two conflict.[3]
Out of scope
This article does not cover Mozilla’s hosted consumer services, such as Mozilla VPN, Mozilla Monitor, Firefox Relay and MDN Plus, which have their own terms of service. It also does not cover Mozilla website content licensing beyond noting that Creative Commons licences apply,[3] the licences of individual third-party components, or legal interpretation of the MPL beyond what the licence text and the licence steward’s FAQ say.