Senior Software Engineer

Join to apply for the Senior Sofware Engineer (Localization) role at Mozilla . 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. About This Team And Role The Localization Team manages the infrastructure that powers localization across all Mozilla products and services, and supports our global community of volunteer localizers. As a Senior Engineer, you’ll contribute to a range of Mozilla localization projects and technologies – from Pontoon, our Django‑based Translation Management System, to open source libraries like moz‑l10n. You’ll also engage with development of standards such as Unicode MessageFormat and work on internationalization features that shape the experience of Firefox and other Mozilla products. You’ll contribute to architectural discussions and help drive feature development within the team. At Mozilla, Senior Engineers are expected to work independently on well‑defined projects, collaborate closely with peers, and play a key role in delivering high‑quality software that advances the team’s goals and Mozilla’s mission. What You’ll Do Contribute to the development of Python and JavaScript libraries (such as moz‑l10n) and tools that support Mozilla’s localization infrastructure. Collaborate with engineers and program managers to design and implement new Pontoon features, across both the front‑end and back‑end. Improve internationalization within the Firefox codebase to make features more adaptable and accessible across languages and regions. Contribute to discussions shaping Mozilla’s positions on internationalization and localization standards. Engage with our community of volunteer developers and localizers to support and guide Mozilla’s localization efforts. Collaborate effectively with teammates and internal clients across regions and time zones. What You’ll Bring Strong experience developing and maintaining web applications and tools using Python and JavaScript. Solid understanding of web technologies, APIs, and modern development workflows. Experience with internationalization (i18n) and localization (l10n) concepts, tools, or workflows. Ability to collaborate effectively in a distributed team, across time zones and disciplines. Excellent communication skills, with an emphasis on clarity and working across technical and non‑technical roles. Commitment to our values: Welcoming differences Being relationship‑minded Practicing responsible participation Having grit Bonus Points Fluency in another language and understanding of linguistic diversity (e.g., grammar, plurals, text direction, and cultural conventions). Experience with open‑source development practices and community collaboration. Programming experience in Rust and C++. 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 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. Hiring Ranges Remote Spain – €57.000—€77.000 EUR Seniority level Associate Employment type Full‑time Job function Engineering and Information Technology Industries Software Development #J-18808-Ljbffr