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Senior Software Engineer, Add-Ons

Mozilla· Firefox
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Hybrid (Spain)€58k - €77kfull-timePosted 1mo ago

About the role

Senior Software Engineer role focusing on the Add-ons ecosystem (AMO) at Mozilla, delivering features, improving platform architecture, and accelerating review/moderation workflows for Add-on developers, with emphasis on Python/Django, CI/CD, observability, and platform reliability.

Responsibilities

  • 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.
  • Feature development: submission flows, trust and safety signals, DevHub and Reviewer tools modernization.
  • AMO application systems: Python/Django, MySQL, React/TypeScript, and asynchronous processing systems.
  • Internal developer platforms: tools to help teams ship and operate software safely and consistently.
  • Team Process: contribute to ceremonies, process improvements, and provide feedback on team effectiveness.
  • Engineering standards: production readiness, testing, recoverability, documentation, safe deployment.
  • Platform reliability: deployments, monitoring, incident response.

Qualifications

  • Strong hands-on experience building and maintaining production applications with Python/Django.
  • Experience operating and improving production software systems with focus on reliability and safe delivery.
  • Strong experience with CI/CD systems and declarative infrastructure as code.
  • Experience designing or improving automated testing and deployment workflows, including integration testing and staged or progressive delivery.
  • Strong understanding of observability (metrics, logging, tracing, SLOs, alerting).
  • Experience building or maintaining internal tools or platforms used by other engineering teams.
  • Experience defining or improving engineering practices (code review standards, operational readiness, runbooks, incident response, on-call, definitions of done).
  • Ability to read unfamiliar codebases and trace behavior across frontend, backend, async jobs, data stores, and infrastructure.
  • Experience debugging complex production issues and driving lasting improvements.
  • Strong technical writing skills (design documents, ADRs, runbooks, incident reports).
  • Experience working with a visible backlog and stakeholder feedback leading to concrete improvements.
  • Strong collaboration and communication in a distributed team.
  • Willingness to mentor peers in operational and reliability practices.
  • Commitment to Mozilla values: welcoming differences, relationship-minded, responsible participation, grit.

Skills

Required:PythonDjangoCI/CDObservabilityTesting/Deployment automationPlatform reliabilityDocumentation

Benefits

  • Generous performance-based bonus plans
  • Rich medical, dental, and vision coverage
  • Generous retirement contributions with 100% immediate vesting
  • Quarterly all-company wellness days
  • Country-specific holidays plus a birthday day off
  • One-time home office stipend
  • Annual professional development budget
  • Quarterly well-being stipend
  • Generous paid parental leave
  • Employee referral bonus program
  • Other benefits (life/AD&D, disability, EAP, etc. - varies by country)
Last updated Sep 16, 2026. Interested? Apply on the company site.

About Mozilla

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Mozilla is the not-for-profit behind the lightning fast Firefox browser. We put people over profit to give everyone more power online.

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