Add-ons have been a part of Firefox since its first version, and they have been integral to its success. The power of the add-on platform and the openness of its ecosystem are key factors that have allowed add-ons to thrive and become one of the most important features in Firefox and other Mozilla applications. Developing add-ons is one of the ways in which you can make a significant and lasting contribution to the Mozilla Mission.
The add-ons platform
The Mozilla add-ons platform is unique in that it is the same platform on top of which front-end application code is written. Firefox code runs alongside add-on code to define how Firefox looks and behaves, and most parts of the Firefox interface can be changed completely with the help of extensions and themes. Innovative add-ons like NoScript and Tree Style Tab would not exist without such an open development platform.
Given the complexity of modern web browsers, add-on developers have a very rich set of APIs to work with. Their breadth can be overwhelming, which is why a simpler set of APIs are provided through the Add-on SDK. The SDK allows you to quickly get started and create good add-ons that cover the most common use cases, while still allowing you to break out of its boundaries and use the low-level APIs available to all extensions.
The Firefox add-on platform extends to Firefox for Android. Depending on the features you want to implement, you can even use the same codebase for your mobile and desktop versions.
Working on add-ons can also serve as a stepping stone to understanding and working on Firefox front-end code. Many add-on developers are regular contributors to Mozilla code, making improvements that help other add-on developers and expanding into areas like security and stability.
The add-ons ecosystem
The main distribution channel for Mozilla add-ons is addons.mozilla.org (AMO). Add-ons listed on AMO are code-reviewed and tested by a team of volunteer add-on developers to ensure they are safe and provide a good user experience. However, Mozilla doesn’t restrict add-on distribution to AMO. Add-on developers are free to distribute their add-ons independently and freely, as long as they follow our Add-on Guidelines.
Add-ons are commonly created with open source principles in mind, so there’s a vast library of current and past add-on work that you can build upon. This also allows developers to continue development of add-ons that can no longer be maintained by their creators or branch existing add-ons in new directions.
Community
There’s a large and active add-on developer community that can help you get started and answer your questions. See the Community and Support section in the sidebar for more information.
Add-on developers are very valuable members of the Mozilla community. The AMO Reviewer Team is composed of experienced add-on developers, and their contributions are rewarded with incentives and invitations to Mozilla events. Many add-on developers have achieved success due to their work or have eventually joined Mozilla as employees.
Creating add-ons helps the Mozilla community grow. It gives our users more tools to customize Firefox and make it their own, continuing its reputation as the most customizable web browser.