• Design & implement features robust enough for our exploding scale. • Drive the implementation of new features - break down complex problems into their bare essentials, translate this complexity into elegant design, and create high-quality, maintainable code. • Create and maintain test automation to enable continuous integration and development velocity. • Design & deliver thoughtfully crafted REST APIs to drive the interactions between our client applications and backend services. • Collaborate and mentor other engineers while providing thoughtful guidance using code, design, and architecture reviews. • Work cross-functionally with other teams (data science, design, product, marketing, analytics). • Leverage a broad skill set and help us implement and learn new technologies quickly. • Provide and receive design and implementation evaluations and improve with each iteration. • Debug production issues across our services infrastructure and multiple levels of our stack. • Think about distributed systems & services and care passionately about producing high-quality code.

• Design, build, and maintain highly scalable and resilient microservices • Implement and manage robust monitoring and alerting systems using Datadog • Utilize Infrastructure as Code (IaC) tools for cloud infrastructure provisioning • Provide technical leadership in system design and architecture • Participate in operational reviews, post-mortems, and reliability initiatives

Title: Senior Software Engineer, WebExtensions Location: Remote US Category: Firefox 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: The WebExtensions platform powers the add-ons ecosystem in Firefox, enabling millions of users to customize their browser while keeping safety and performance at the forefront. As a WebExtensions Engineer, you will help implement new extension capabilities, improve existing APIs, and ensure that extensions remain reliable across Firefox. As a Software Engineer on the WebExtensions team, you’ll bring a passion for exploring complex systems and creating experiences that balance developer power with user trust. You’ll work deep in the Gecko platform to evolve extension capabilities, and you’ll build UI features in Firefox that make extensions clear and manageable for users. Along the way, you’ll collaborate with experts across Mozilla and help advance cross-browser compatibility and the path toward standardization. Your work will keep extensions safe, powerful, and reliable for developers and millions of Firefox users. What you’ll do: - Implement and maintain WebExtensions APIs and Addon Management, balancing power, safety, and performance, as well as user interfaces in Firefox. - Debug and fix issues affecting extensions in Firefox. - Collaborate with product managers, QA, and the AMO engineering team to deliver features end-to-end. - Contribute to Mozilla-owned extensions and system add-ons. - Participate in open source workflows: code reviews, pull requests, and discussions in Bugzilla/GitHub. - Support extension developers by helping diagnose issues and improving tooling/documentation. What you’ll bring: - 4+ years of professional experience in software development. - Strong proficiency in JavaScript, DOM APIs, HTML, and CSS. - Familiarity with modern browser architecture and debugging tools. - Experience with API design and integration. - Ability to navigate and learn from large codebases. - Strong communication skills and experience collaborating in distributed teams. - Bonus points for: - Experience with Firefox internals, C++ or Rust. - Familiarity with Android or GeckoView development. - Knowledge of web security principles. - Contributions to open source projects, especially in browser or extension development. 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 hiringaccommodation@mozilla.com 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 Hiring Ranges: US Tier 1 Locations $137,000 - $183,000 USD US Tier 2 Locations $126,000 - $168,000 USD US Tier 3 Locations $116,000 - $155,000 USD

• Lead the migration of services from our monolithic codebase to a distributed microservices architecture—designing for scalability, reliability, and long-term maintainability. • Design and build microservices that integrate cleanly into our broader distributed system, with strong attention to observability and fault tolerance. • Apply sound architectural patterns across APIs, database schemas, and event-driven systems—making decisions that won’t box the team in as we scale. • Anticipate where architectural decisions create downstream risk, raise them early, and bring a concrete path forward. • Deliver production-ready code at a high cadence—contributing meaningfully within the first 30 days and sustaining that pace as scope grows. • Write advanced, adaptable code that captures the core essence of the solution and holds up as requirements evolve. • Identify and resolve production issues—individually or as part of a team—and take technical ownership of the health of systems you touch. • Distinguish reversible from irreversible decisions and act accordingly: move fast where it’s safe to, slow down where it matters. • Serve as a technical partner in cross-functional settings—representing the engineering perspective to technical and non-technical audiences with clarity. • Work collaboratively with product, design, and data science to ship solutions that meet patient and business needs. • Communicate progress, blockers, and risks proactively—not at the deadline. • Mentor and coach mid-level and senior engineers—helping them grow their craft through direct feedback, pairing, and code review. • Role model high technical, cultural, and process standards: quality is the baseline, not the goal. • Continuously build and share domain expertise—turning what you learn into leverage for the team. • Actively use AI tools (e.g., ChatGPT, Claude, Gemini) to accelerate design, code generation, debugging, and documentation—with a clear point of view on where AI helps and where human judgment is non-negotiable. • Review AI-generated outputs critically before acting on them—take personal accountability for everything you ship, regardless of how it was produced. • Share what’s working and what isn’t with your team—AI fluency grows collectively, not just individually.