About the Team & RoleThe 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)
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
