Senior Software Engineer, Add-Ons

Mozilla; España; Remote; EUR 70,000 - 100,000; Full time

Job summary

Mozilla Corporation is seeking a Senior Software Engineer to advance the Add-ons ecosystem (AMO) by delivering major features, modernizing DevHub, and strengthening reviewer tooling for millions of Firefox users.

You will work with engineers, reviewers, developer support and product leadership to build resilient systems, improve CI/CD, observability, and deployment reliability across Python/Django, MySQL, and React/TypeScript stacks.

Qualifications

• Proven experience building production apps with Python/Django.
• Strong CI/CD experience and infrastructure as code.
• Deep knowledge of observability, monitoring, and incident response.

Responsibilities

• Deliver major features and architectural improvements across the Add-ons stack.
• Establish and maintain engineering standards across code review, deploy readiness, and runbooks.
• Create robust observability systems and data-backed insights.
• Provide peer feedback and help others grow.
• Improve CI/CD pipelines and declarative infrastructure.

Skills

Python

Django

CI/CD

Observability

Code Review

Testing

Tools

React/TypeScript

MySQL

DevHub

IaC

Job description

Why Mozilla?

Mozilla Corporation is the non-profit-backed technology company that has shaped the internet for the better over the last 25 years. We make pioneering brands like Firefox, the privacy-minded web browser. Now, with more than 225 million people around the world using our products each month, we’re shaping the next 25 years of technology and helping to reclaim an internet built for people, not companies. Our work focuses on diverse areas including AI, social media, security and more. And we’re doing this while never losing our focus on our core mission - to make the internet better for people.

The Mozilla Corporation is wholly owned by the non-profit 501(c) - Mozilla Foundation. This means we aren’t beholden to any shareholders - only to our mission. Along with thousands of volunteer contributors and collaborators all over the world, Mozillians design, build and distribute open-source software that enables people to enjoy the internet on their terms.

About this team and role:

addons.mozilla.org (AMO) is the foundation of the Firefox add-ons ecosystem. It's a showcase for developers to publish and grow their extensions, and a place of discovery for millions of users who customize Firefox to make it their own. Behind the scenes are the DevHub which enables developers to manage their extensions. To manage the ecosystem there are a series of Reviewer tools and automated moderation systems.

As a Senior Software Engineer, you'll bring a passion for crafting resilient systems that accelerate our review and moderation teams to provide a first-class experience for Add-on developers. You'll work closely with engineers, reviewers, developer support, and Add-ons leadership to turn ideas into polished features, modernize the platform and its architecture, and see your work reach millions of people around the world.

What you'll do:

• Deliver major features and architectural improvements across the Add-ons stack, including automated moderation pipelines, Reviewer tools, and DevHub.
• Help establish and maintain engineering standards across areas such as code review, definition of done, production readiness, runbooks, incident response, on-call practices, coding conventions, and infrastructure as code.
• Create robust observability systems and data-backed insights.
• Provide peer feedback, share knowledge and help others grow.
• Build and improve the systems that enable Add-ons engineering to safely develop, deploy, observe, and operate production services.
• Improve our CI/CD pipelines using declarative, pipeline-as-code approaches that make changes reproducible, testable, and easy to review.
• Deliver work iteratively using a visible backlog, short feedback cycles, retrospectives, and demonstrations to stakeholders.
• Write clear technical documentation, including design notes, Architecture Decision Records, runbooks, and incident write-ups.
• Work effectively in unfamiliar codebases, tracing requests and asynchronous jobs end-to-end to understand failures and identify opportunities for improvement.
• Collaborate with designers, product managers, QA, and community contributors to deliver end-to-end improvements.
• Contribute in the open through pull requests, code reviews, and discussions.
• Work on:
  • Feature development: submission flows, trust and safety signals, DevHub and Reviewer tools modernization.
  • AMO application systems: Work within our Python/Django, MySQL, React/TypeScript, and asynchronous processing systems.
  • Internal developer platforms: Create tools and paved paths that make it easier for teams to ship and operate software safely and consistently.
  • Team Process: Contribute to team ceremonies, execute process improvement, and provide feedback on team effectiveness.
  • Engineering standards: Help make production readiness, testing, recoverability, documentation, and safe deployment part of the normal development lifecycle.
  • Platform reliability: Deployments, monitoring, and incident response.

What you'll bring:

• Strong hands-on experience building and maintaining production applications with Python/Django.
• Experience operating and improving production software systems where reliability and safe delivery matter.
• Strong experience with CI/CD systems and treating pipelines and infrastructure declaratively as code.
• Experience designing or improving automated testing and deployment workflows, including integration testing and staged or progressive delivery.
• Strong understanding of observability as an engineering discipline, including metrics, logging, tracing, service-level objectives, and actionable alerting.
• Experience building or maintaining internal tools or platforms used by other engineering teams, with an understanding that internal systems have users, reliability expectations, roadmaps, and lifecycle considerations.
• Experience defining or improving engineering practices such as code review standards, operational readiness, runbooks, incident response, on-call expectations, or definitions of done.
• Ability to read and understand...