Senior Software Engineer, Firefox Security

Mozilla; Paris; Remote; EUR 53,000 - 71,000; Full time

Benefits offered by this job

Performance bonus

Retirement contributions

Wellness days

Birthday day off

Home office stipend

Professional development budget

Parental leave

Employee referral bonus

Life/AD&D

Disability insurance

EAP

Job summary

Mozilla is seeking a security-focused systems programmer to design, build, and ship enterprise-grade security features for Firefox across multiple operating systems. You will advance Firefox’s security architecture and contribute to cryptographic, WebPKI and security-sensitive APIs while collaborating with distributed teams.

Join Mozilla to improve browser reliability, performance, and security posture, with a focus on strong code quality and scalable engineering practices.

Qualifications

• Systems programming experience and security knowledge: 3+ years of experience in low-level software engineering, strong proficiency in C and/or C++, and a solid understanding of security fundamentals.
• Debugging and problem-solving skills: Experience diagnosing issues in multithreaded, cross-platform native applications, including memory and performance challenges.
• Web platform and modern systems experience: Familiarity with web technologies (HTML, CSS, JavaScript) and interest or experience in Rust; ability to work in large, multi-language codebases.
• Effective collaboration and communication: Experience working with distributed teams and communicating technical ideas clearly.

Responsibilities

• Design, build and implement security and hardening features for enterprise users across Firefox.
• Advance Firefox’s security architecture across multiple operating systems and improve core security mechanisms.
• Contribute to security initiatives: investigate issues, identify root causes, and deliver fixes.
• Improve browser reliability and performance: diagnose and resolve issues affecting stability and memory usage.

Skills

3+ years systems programming

C and/or C++

security fundamentals

multithreaded debugging

web technologies (HTML, CSS, JS)

Rust interest/experience

distributed teamwork

clear written and verbal communication

Job description

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

• Design, build and implement security and hardening features for enterprise users: Design, implement, test, and ship cutting-edge security features that strengthen Firefox’s security posture.
• Advance Firefox’s security architecture across multiple operating systems: Contribute to and drive cutting-edge improvements to Firefox’s core security posture, by building privilege isolation and moving trust boundaries or Strengthen Firefox’s security architecture: Improve Firefox’s core security mechanisms including cryptographic protocols, WebPKI, and security-sensitive web APIs.
• Contribute to our security initiatives: Work across teams to investigate security issues, identify root causes, and deliver robust, maintainable fixes.
• Improve browser reliability and performance: Diagnose and resolve issues affecting stability, correctness, performance, and memory usage in a complex, multithreaded environment.

What You’ll Bring

• Systems programming experience and security knowledge: 3+ years of experience in low-level software engineering, strong proficiency in C and/or C++, and a solid understanding of security fundamentals.
• Debugging and problem-solving skills: Experience diagnosing and resolving issues in multithreaded, cross‑platform native applications, including memory and performance challenges.
• Web platform and modern systems experience: Familiarity with web technologies (HTML, CSS, JavaScript) and interest or experience in Rust; ability to work effectively within large, complex, multi‑language codebases.
• Effective collaboration and communication: Experience working with distributed teams and communicating technical ideas clearly in writing and conversation.

What You’ll Get

• Generous performance‑based bonus plans to all eligible employees - we share in our success as one team
• 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 stipendConsiderable 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 [e-mail] 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

Req ID: R3247

Hiring Ranges

Remote France

€53.000—€71.000 EUR