Senior Software Engineer, Firefox Security

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. 

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.

What you’ll do: 

• Advance Firefox's security architecture and cryptography stack: Contribute to improvements in Firefox's core security systems, with a focus on cryptographic protocols, WebPKI, and security-sensitive web APIs. Help implement and maintain security features that support the evolution of public key infrastructure on the web.
• Design and implement web platform security features: Develop and ship web platform features in collaboration with teammates and the broader web community. Contribute to standards-based, secure, and interoperable implementations across Firefox.
• Improve browser reliability, performance, and resource efficiency: Investigate and resolve issues impacting stability, correctness, and performance. Analyze and improve memory usage and efficiency within a complex, multi-threaded browser environment.
• Collaborate on security initiatives: Partner with engineers across teams to identify, prioritize, and address security issues. Participate in debugging, root cause analysis, and implementation of effective long-term solutions.
• Contribute to technical design and planning: Participate in technical discussions, design reviews, and project planning for security-related initiatives. Help evaluate tradeoffs and contribute to engineering decisions within your area of work.

What you’ll bring: 

• Strong software engineering and security fundamentals: Experience in software engineering, with proficiency in C/C++ and a solid understanding of security principles, including cryptographic protocols and implementations.
• Experience building and maintaining complex software systems: Ability to contribute to the design, implementation, testing, and maintenance of software in large-scale or security-sensitive environments.
• Strong debugging and problem-solving skills: Expertise in diagnosing and resolving issues in multi-threaded, cross-platform native applications, including performance and memory-related challenges.
• Collaborative and effective communicator: Ability to work effectively with distributed teams, communicate technical concepts clearly, and collaborate constructively to solve problems.
• Growth mindset and willingness to learn: Demonstrated curiosity and desire to deepen expertise in browser security, cryptography, and systems programming while continuously improving engineering skills.
• Web platform and modern systems experience: Familiarity with web technologies and interest or experience in Rust. Comfortable working within large, complex, multi-language codebases.

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