Senior Software Engineer, Add-Ons

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 unfamiliar codebases and trace application behavior across frontend, backend, asynchronous jobs, data stores, and infrastructure.
Experience debugging complex production issues and turning what you learn into lasting system improvements.
Strong technical writing skills, with experience creating useful documentation such as design documents, ADRs, runbooks, and incident reports.
Experience working iteratively with a visible backlog, regular stakeholder feedback, and retrospectives that result in concrete improvements.
Strong collaboration and communication skills in a distributed team environment.
A willingness to share knowledge and mentor peers in operational and reliability practices.
Commitment to our values:Welcoming differences
Being relationship-minded
Practicing responsible participation
Having grit


Bonus points for:Experience with Google Cloud and operating Kubernetes.
Experience with infrastructure-as-code tooling and policy-as-code.
Experience establishing SLOs and error-budget-based reliability practices.
Experience with chaos engineering, disaster recovery testing, or production readiness reviews.
Experience with trust and safety, automated moderation, abuse prevention, or other adversarial systems.
Contributions to open source projects

What you'll get:Generous performance-based bonus plans to all eligible employees - we share in our success as one team
Rich medical, dental, and vision coverage
Generous retirement contributions with 100% immediate vesting (regardless of whether you contribute)
Quarterly all-company wellness days where everyone takes a pause together
Country specific holidays plus a day off for your birthday
One-time home office stipend
Annual professional development budget
Quarterly well-being stipend
Considerable paid parental leave
Employee referral bonus program
Other benefits (life/AD&D, disability, EAP, etc. - varies by country)

About Mozilla

Mozilla exists to build the Internet as a public resource accessible to all because we believe that open and free is better than closed and controlled. When you work at Mozilla, you give yourself a chance to make a difference in the lives of Web users everywhere. And you give us a chance to make a difference in your life every single day. Join us to work on the Web as the platform and help create more opportunity and innovation for everyone online.

Commitment to diversity, equity, inclusion, and belonging

Mozilla understands that valuing diverse creative practices and forms of knowledge are crucial to and enrich the company's core mission. We encourage applications from everyone, including members of all equity-seeking communities, such as (but certainly not limited to) women, racialized and Indigenous persons, persons with disabilities, persons of all sexual orientations, gender identities, and expressions.

We will ensure that qualified individuals with disabilities are provided reasonable accommodations to participate in the job application or interview process, to perform essential job functions, and to receive other benefits and privileges of employment, as appropriate. Please contact us at [email protected] to request accommodation.

We are an equal opportunity employer. We do not discriminate on the basis of race (including hairstyle and texture), religion (including religious grooming and dress practices), gender, gender identity, gender expression, color, national origin, pregnancy, ancestry, domestic partner status, disability, sexual orientation, age, genetic predisposition, medical condition, marital status, citizenship status, military or veteran status, or any other basis covered by applicable laws. Mozilla will not tolerate discrimination or harassment based on any of these characteristics or any other unlawful behavior, conduct, or purpose.

Group: D

#LI-REMOTE

Req ID: R3023

Hiring Ranges:

Remote Finland

€45.000-€60.000 EUR