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Senior Software Engineer, Firefox Security

Mozilla· Firefox
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Hybrid (France)€53k - €71k-full-timePosted 6d ago

About the role

Senior software engineer focused on designing, building, and improving security features and architecture for Firefox, with emphasis on enterprise security, cross-OS hardening, and performance/reliability in a large, multi-language codebase.

Responsibilities

  • 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 by improving 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.

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 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.

Skills

Required:CC++Security fundamentalsMultithreaded debuggingWeb technologiesCommunication
Nice to have:Rust

Benefits

  • 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 stipend
  • Considerable paid parental leave
  • Employee referral bonus program
  • Other benefits (life/AD&D, disability, EAP, etc. - varies by country)
Last updated Oct 21, 2026. Interested? Apply on the company site.

About Mozilla

Internet for people, not profit

Mozilla is the not-for-profit behind the lightning fast Firefox browser. We put people over profit to give everyone more power online.

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