Mozilla & the Rebel Alliance

An representation of Mozilla's contributor communities

The full report is available as a pdf-file here.

Mozilla’s success relies upon the strength of our rebel alliance: the always evolving set of individual and organizational contributors who help us build the products and services that empower users in their digital lives and who fight with us for a healthier internet.

Supporting and engaging this rebel alliance begins with understanding it. Along with our partners Analyse & Tal, Bitergia and Open Tech Strategies, Open Innovation has published a comprehensive “Mozilla and the Rebel Alliance” report* to provide a holistic view of our contributor ecosystem’s network structure, health and impact. This is an update to the report we did in 2017 in which we discovered that -- contrary to internal opinion -- there is no one Mozilla community but many, distinguished by areas of contribution, motivations, engagement levels, and more. This year, we’re able to visually describe these distinct contributor communities as well as how they are interconnected. We’ve also developed a rudimentary framework, open to refinement, for describing the ‘health’ of our contributor communities.

Building upon our previous work, we’ve analyzed quantitative and qualitative data from six essential contributor communities and platforms: Git and GitHub, Bugzilla, Kitsune (SUMO), Pontoon (Localization), Kuma (Mozilla Developer Network) and Add-ons.

Our contributor communities are generally healthy and strong, but it’s up to all of us to continue building, engaging and supporting this rebel alliance.

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*This report was created in accordance with Mozilla's privacy policy.

The Rebel Alliance Network

This network shows where 22,821 contributors participated across Mozilla's ecosystem between 2017-2019.

Contributors are grouped into segments based on their activity. Each circle represents a casual, regular or core contributor, which is connected to one or more projects. Click on one to see more.

We have analyzed contributions from some affiliate groups in Mozilla, such as: mozillians, tech speakers, mission driven mozillians and OSSN.

Select contributor segment:

Interested in a specific project? Have a look at one of these 49 projects (we've only included detailed information on 10 of them).

for a detailed description of this work and methodology.

Data: non-employee contributions (2017-2019)
Network View with Contributor Segments

With more than 2 million contributions from 22,821 non-employee contributors between 2017-2019, Mozilla has a Rebel Alliance that’s vibrant, active, and impactful.

This network view shows contributors between 2017-2019 as defined by their segment, or their total lifetime amount of contributions (casual, regular, core). The node (circles) represent contributors, and the edges (lines) represent contributions from contributors to different Mozilla projects. Contributors are attributed to the project to which they most contribute. The graph shows where contribution across projects occurs, which can be filtered by contributor segment to highlight their different pathways (see pull down menu/filter). This analysis includes only non-employee contributors who made more than 5 contributions during this time period -- in other words, no ‘visitors’.

In the center of the network, we find an extremely productive group of core and regular contributors who are active on multiple projects. Non-employee core contributors contribute to an average of 4.3 projects, and non-employee regular participants contribute to an average of 2.5 projects.

Some of the big projects (larger labels) are placed at the periphery because they have a large community of non-employee contributors who only participate in that specific project (e.g. Firefox, Thunderbird, MDN). Projects that are placed closer together share many contributors.

In general, the more connections in a network, the stronger it is. By this view, contributor communities in Mozilla’s Rebel Alliance are generally well connected and robust.

The full report dives more deeply into the ‘health’ of ten Mozilla sponsored open source projects. This graph shows a short selection of insights related to these contribution areas - just select a project. Note that where we highlight attraction and retention numbers, they are specific to that particular project and do not indicate that those who no longer participate in that project aren’t continuing to participate in other contribution areas.

Data sources and definitions

This network was created by gathering and analyzing activity data from the following platforms and communitites: Git and GitHub, Bugzilla, Kitsune (SUMO), Pontoon (Localization), Kuma (Mozilla Developer Network) and Add-ons.

For this upcoming report, we developed platform specific definitions based on lifetime contribution activity (see table below). This method enables us to create more granular and meaningful segments that take into account the different natures of each platform and contribution types (code, translations, questions, articles, etc.).

Contributors were defined as casual, regular or core if they made a certain threshold of contributions over their lifetime of contribution to that particular platform. The segment definitions were developed based on all contributions to the platform, also including contributions from employees.

Table: Platform specific contributor segment definitions. Numbers are registered contributions within each platform.
Segment Git/GitHub Bugzilla Kuma Kitsune Pontoon Add-ons
Core >1,000 >1,000 >1,000 >250 >1500 >50
Regular 100 - 1,000 100 - 1,000 100 - 1,000 21 - 250 201 - 1,500 21 - 50
Casual 6 - 99 6 - 99 6 - 99 6 - 20 6 - 200 6 - 20

The Rebel Alliance Network: by project activity


Firefox MDN Thunderbird Gecko Rust Add-ons/Web extensions Web Properties Firefox Android Others

The Rebel Alliance colored by project activity

This network is based on the same data sources as the interactive graph above. The nodes represent contributors and the edges (lines) represent contributions from contributors to different Mozilla projects. Each contributor is coloured by the project, which most of their contributions go to. In this way, we can talk about project communities.

In the centre of the network, we see the same extremely active group who contribute on several different projects, however as the purple colour represent – a lot of these people have most of their contributions to Firefox.

We can also identify some overlapping groups – such as Firefox and Gecko. They both have their own community of people not contributing to any other projects, but they also have contributors scattered around the network contributing to various different project. As such, both projects are fairly robust and benefit from the diversity of knowledge and experience that the contributors get from taking part in Mozilla's Rebel Alliance.

Mozilla’s External Network Influence

External repos

GitHub API. Other public repositories Mozilla contributors participated in, as defined by issues, commits, and pull requests. We only considered public repositories that had more than five unique Mozilla contributors within the time period 2017-2019. In total, we registered 3.1 million contributions, from 7,041 non-employee Mozilla contributors to 5,377 other repositories.

Mozilla’s rebel alliance helps us influence the industry, share expertise, gain more diverse views, align upstream dependencies and encourage downstream adoption.

This network graph shows to which other GitHub projects Mozilla participants also contribute to, giving us an indication of the ecosystem of open source projects around our contributor communities and the relative strength of the connections through overlaps in contribution.

The yellow cluster represents projects which tend to be run by individuals rather than organizations. Here we also find a few Rust specific projects, but we also find Linux specific projects which border to the blue cluster.

The green cluster encompases a wide range of web technologies and web development tools, such as node.js, react, angular, vue.js, npm, babel, webpack and bootstrap. But we also find tools such as Visual Studio Code, Atom and Electron.

The blue cluster holds programming languages such as Go and Python, but also infrastructure projects such as Kubernetes and Ansible. On the edges of this cluster, we also find Homebrew and Travis, as well as ecosystems of repositories connected to operating systems.

The pink cluster to the right includes web standardization work, including repositories from the W3C and the WHATWG community. The top of this cluster also holds different 3D and VR/MR repositories, such as three.js and gITF.

Finally, the purple cluster at the top is more or less an ecosystem of repositories around ember.js, although we also find Rails in this cluster.

External organizations
External Organizations

When looking at the organizational owners behind these repositories, we see the other main organizations with which Mozilla non-employee contributors engage (same time period, 2017-2019). This network graph ties organizations together based on the activity of Mozilla contributors.

The size of the circles represents the number of contributors who have engaged with an organizations' repositories, as measured by commits, issues and pull requests.

Mozilla non-employee contributors engage most with Microsoft open source projects, with 1,000 contributors, closely followed by Google (685) and Facebook (662). Node, Homebrew, npm, W3C and GitHub are other organizations which also stands out.

Mozilla Project Communities


This network includes non-employee contributors who have contributed to Firefox between 2017-2019. It visualizes 12,334 contributors (circles) and their 1.9 million contributions across Mozillas platforms and communitites (edges).

The network shows which other projects contributors to Firefox also engage in. Here, both Gecko and Thunderbird are the main projects, but we also find Web Properties, Add-ons/Web Extensions and MDN.

The Firefox project is the biggest project in terms of number of contributors. It is mainly made up of non-staff contributors.

A great share of the people contributing to Firefox do not contribute to any other projects (they are gathered in the lower part of the network only connected to ”Firefox”). However, especially the core segment is also very active on other projects.

What counts as a contribution? For Firefox we have registered contributions from Bugzilla, GitHub, AMO, Kitsune and Pontoon. As such, this visualization includes both code and non-code contributions.

Firefox contributors

Contributors are grouped into segments based on their activity. Each circle represents a casual, regular or core contributor.

Gecko contributors

Contributors are grouped into segments based on their activity.
Each circle represents a casual, regular or core contributor.


This network includes non-employee contributors who have contributed to Gecko between 2017-2019. It visualizes 2,680 contributors (circles) and their 360,000 contributions across Mozillas platforms and communitites (edges).

The network shows which other projects contributors to Gecko also engage in. Here especially Firefox is the main project, but we also find MDN, Infrastructure and Rust among others.

The contributions to Gecko are equally coming from casual, regular and core segments, implying a high degree of diversity

As the network shows, the people contributing to Gecko are often also active on several other projects – and this is true for all three segments.

What counts as a contribution? For Gecko we have registered contributions from Bugzilla and GitHub.


The research for this report was executed in partnership with our data provider, Bitergia, a software development analytics company that specializes in open source analytics, with whom we also worked on the 2017 communities and contributors report. This year, we expanded the collaboration to include Analyse & Tal, an employee-owned, co-operative data analytics and visualization firm.

This research followed Mozilla’s privacy policy and lean data practices, meaning we only collected data that were required to deliver valuable insights, we protected these data through strong security, and we informed our communities of the work through direct messages and our privacy policy. No private, personally identifiable information was shared with our partners.

We worked with product teams and community managers across the organization to be sure we were looking at the right set of repositories and linking contribution from Pontoon (localization) and Kitsune (support) to the right products and projects. We did not include repositories we knew were dead or otherwise invalid (e.g. forks).

However, there are surely inaccuracies that need to be remedied in the future. In some areas, there were repos that were hard to categorize in the timeframe we had for this report. The GitHub repos and Bugzilla categorization we used for this report can be found here, and we welcome all feedback at

A note on the Infrastructure and Web Properties contribution categories. These are both somewhat catch-alls for GitHub repos and Bugzilla issues that are related either to IT infrastructure, such as cloud-based services for Firefox, or content and code for some of Mozilla’s websites. These categories should be better vetted in future reports to ensure a more accurate representation of Mozilla contribution. For example, non-employee contribution to some of the cloud-based services for Firefox might be better categorized as contributions to Firefox.