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<

Senior Machine Learning Engineer, Applied AI Modeling at Mozilla