Senior Machine Learning Engineer, Applied AI Modeling

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, and Pocket, a service for keeping up with the best content online. 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 the Team & Role The Firefox team is building the next generation of intelligent, privacy-aware experiences for the web. As part of this evolution, we are embedding modern AI and LLM-driven features directly into the browser—empowering users while safeguarding their autonomy and data. We’re looking for a Senior Machine Learning Engineer with a strong focus on applied AI and modern LLM-based applications. You will help conceptualize, prototype, and deploy user-facing experiences grounded in Generative AI, working collaboratively with engineering, design, and product to bring these capabilities to life in Firefox. What You’ll Do Develop and fine-tune large language models (LLMs) for intelligent, safe, and responsive browser interactions. Apply retrieval-augmented generation (RAG), summarization, classification, and intent modeling techniques in real-world browser workflows. Use modern ML tooling (e.g., Hugging Face, LangChain, Weights & Biases, Ray, or similar) to support end-to-end model development, including experimentation, evaluation, and rollout. Collaborate closely with product and engineering partners to design, iterate, and launch features that align with user needs and Mozilla’s values. Design and implement experiments to test model behavior in production, analyze results, and iterate based on findings. Document and share your work, participating in code reviews and team design discussions. What You Bring 4+ years of experience in applied machine learning, with a focus on natural language processing or generative AI. Hands-on experience fine-tuning and evaluating LLMs using modern tools and open-source libraries. Strong understanding of prompt engineering, embedding-based retrieval, and evaluation strategies for generative applications. Experience using ML tooling to lead the end-to-end lifecycle of model development—from data exploration to deployment-ready artifacts. Track record of building user-facing AI features, especially where privacy, latency, and usability are critical. Clear communication skills and ability to collaborate with multi-functional partners on a distributed team. Commitment to our values: Welcoming differences Being relationship-minded Practicing responsible participation Having grit Bonus Skills Familiarity with on-device model optimization or privacy-preserving ML. Experience working in a browser context or with web technologies. Contributions to open-source ML frameworks or model hubs. 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 Req ID: R3070 Hiring Ranges: US Tier 1 Locations $163,000—$218,000 USD US Tier 2 Locations $150,000—$200,000 USD US Tier 3 Locations $139,000—$185,000 USD