Senior Machine Learning Engineer

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.

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
• Rich medical, dental, and vision coverage
• Generous retirement contributions with 100% immediate vesting
• Quarterly all-company wellness days
• 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)