Senior Software Engineer, Firefox Security - Mozilla

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—all while staying focused 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 worldwide, 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 features: Design, implement, test, and ship cutting-edge security and hardening features that strengthen Firefox’s security posture for enterprise users.
• Advance Firefox’s security architecture: Drive improvements across multiple operating systems by building privilege isolation and moving trust boundaries, or improve core security mechanisms including cryptographic protocols, WebPKI, and security-sensitive web APIs.
• Contribute to 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
• 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
• Paid parental leave
• Employee referral bonus program
• Comprehensive benefits (life/AD&D, disability, EAP, etc.)