Senior Software Engineer (Add-Ons)

Mozilla; Greater London; On-site; GBP 90,000 - 130,000; Full time

Benefits offered by this job

Health and dental

Mental health support

Paid leave

Retirement contribution

Professional development budget

Life/AD&D insurance

Wellbeing stipend

Remote work allowance

Job summary

Mozilla is seeking a Senior Software Engineer to advance the Firefox Add-ons ecosystem, delivering major features across the AMO stack and refining the DevHub and Reviewer tooling. You will help modernize the platform, improve architecture, and reach millions of users globally.

You will uphold engineering standards, build robust observability, and enhance CI/CD with pipeline-as-code. The role requires hands-on Python/Django, Kubernetes, and cloud experience, plus collaboration with product, QA,

Qualifications

• Strong hands-on experience building and maintaining production applications with Python/Django.
• Experience designing or improving automated testing and deployment workflows, including integration testing and staged or progressive delivery.
• Experience with Google Cloud and operating Kubernetes.

Responsibilities

• Deliver major features and architectural improvements across the Add-ons stack.
• 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 on 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, AMO application systems (Python/Django, MySQL, React/TypeScript), internal developer platforms, team process, engineering standards, platform reliability.

Skills

Python/Django

CI/CD

Observability

Documentation

Code reviews

Mentoring

Distributed team

Production debugging

Tools

Google Cloud

Kubernetes

Job description

• 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
• 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

Benefits

• Health and wellness: Mozilla covers medical, dental and vision plan premiums at 100% for U.S. and Canadian employees. Our offerings give you the options you need to manage your health — and your family’s — the way you want.
• Mental health: Mental health is as important as our physical health. That’s why Mozilla’s health benefits include therapy and coaching sessions to make sure our people have access to the care they need.
• Time away: With all of life’s demands, time away from work to disconnect and recharge is essential. In addition to country-specific holidays (12 in the U.S. and Canada), vacation and sick time start accruing right away (specifics vary by country). Everyone also takes a pause together on quarterly all-company wellness days, plus you get to celebrate the most personal holiday of all: your birthday.
• Parental leave: While Mozilla’s parental leave policies vary globally, our U.S. and Canadian-based employees can look forward to 26 weeks of paid leave for childbearing parents and 12 weeks of paid leave for non-childbearing parents.
• Financial: Mozilla is a private company, so our compensation isn’t tied to stock options or equity plans. Instead, we offer generous, performance-based bonus plans to all regular employees to underscore that we share in our success as one team. As for retirement savings for US and Canadian employees, Mozilla contributes a percentage of your eligible base salary each year to the 401(k) Plan/RRSP (regardless of whether you contribute or not), with 100% vesting.
• Learning and development: We’re big believers in learning by doing, and we also want to invest in your education and development beyond your role. Every employee is eligible for an annual professional development budget. Mozillians can put it toward technical or management training, certifications, conferences and more.
• Help when you need it: Life is full of surprises; that’s why it’s important to be prepared. Mozilla provides Life/AD&D and Short and Long Term Disability insurance (offerings may vary by locale) to ensure that you and your family will have a safety net in place should you ever need it.
• Plus a bit more: A few other benefits include a quarterly wellbeing stipend (to use on those things just for you), an employee referral bonus, internet reimbursement if you’re remote, and a budget for office essentials to make working remotely ergonomically comfortable.

• Strong collaboration and communication skills in a distributed team environment
• Experience operating and improving production software systems where reliability and safe delivery matter
• Experience designing or improving automated testing and deployment workflows, including integration testing and staged or progressive delivery
• Strong hands-on experience building and maintaining production applications with Python/Django
• Strong experience with CI/CD systems and treating pipelines and infrastructure declaratively as code
• A willingness to share knowledge and mentor peers in operational and reliability practices
• Strong technical writing skills, with experience creating useful documentation such as design documents, ADRs, runbooks, and incident reports
• Being relationship-minded
• Strong understanding of observability as an engineering discipline, including metrics, logging, tracing, service-level objectives, and actionable alerting
• Experience working iteratively with a visible backlog, regular stakeholder feedback, and retrospectives that result in concrete improvements
• Having grit
• Practicing responsible participation
• 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
• Welcoming differences
• Ability to read and understand unfamiliar codebases and trace application behavior across frontend, backend, asynchronous jobs, data stores, and infrastructure
• Experience defining or improving engineering practices such as code review standards, operational readiness, runbooks, incident response, on-call expectations, or definitions of done
• Commitment to our values:
• Experience debugging complex production issues and turning what you learn into lasting system improvements
• 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
• Contributions to open source projects
• Experience with trust and safety, automated moderation, abuse prevention, or other adversarial systems