[All remote jobs](https://jobicy.com/jobs.md)[![Mozilla logo](https://jobicy.com/data/server-nyc0409/galaxy/mercury/2020/10/mozilla.jpg)](https://jobicy.com/company/mozilla.md)[Mozilla](https://jobicy.com/company/mozilla.md) # Senior Software Engineer, Firefox Security Review the role, location requirements, compensation details, and application process before deciding whether this opportunity fits your next career move. [Apply for this job](#job-application)[View company](https://jobicy.com/company/mozilla.md)ShareRemote from[France](https://jobicy.com/job-region/france.md)SalaryEUR 53k–71k / yrDepartment[Cybersecurity](https://jobicy.com/categories/cybersecurity.md)EmploymentFull TimeExperienceSeniorPublished27 Oct 2026Apply before26 Nov 2026Listing views42Application actions3Application toolkit ## Make your next move. Prepare your resume, explore your fit, and draft a cover letter for this opportunity. AI Summary ## The role, at a glance. Mozilla is seeking a senior engineer to strengthen Firefox security through systems-level design, implementation, testing, and incident investigation. The role focuses on browser hardening, privilege isolation, trust boundaries, cryptographic protocols, WebPKI, and security-sensitive web APIs. The engineer will diagnose stability, memory, correctness, and performance issues in a large multithreaded, cross-platform native codebase. Strong C or C++ skills, security fundamentals, web-platform familiarity, and effective collaboration with distributed teams are central to success. ## Role DNA A quick view of the complexity, pace, ownership and collaboration implied by the job description. ### Job Complexity 5/5EasyHard ### Pace & Pressure 4/5RelaxedFast-paced ### Autonomy Level 4/5GuidedFull ownership ### Communication Load 4/5IndependentCollaborative AI insightThis is a technically demanding browser-security role involving low-level native code, complex trust boundaries, and cross-platform multithreaded systems. Success requires independent debugging and secure design decisions while coordinating fixes across teams. ## Salary analysis Estimated compensation compared with the broader EU market for similar roles. Estimated job median (per year)Market rate€62,000EU market range (per year)€55k–€80k0€88k AI insightThe yearly pay period is inferred from the job context; it was not explicitly stated by the employer. The stated hiring range is €53,000–€71,000 EUR annually; the annual cadence is inferred from the senior full-time engineering role and French market conventions because the posting does not explicitly state a pay period. The estimated market range is €55,000–€80,000 EUR per year. ## Core skills Skills and capabilities most closely associated with this opportunity. [C](https://jobicy.com/jobs?search_keywords=C.md)[C++](https://jobicy.com/jobs?search_keywords=C%2B%2B.md)[Rust](https://jobicy.com/jobs?search_keywords=Rust.md)[Systems programming](https://jobicy.com/jobs?search_keywords=Systems%20programming.md)[Application security](https://jobicy.com/jobs?search_keywords=Application%20security.md)[Browser security](https://jobicy.com/jobs?search_keywords=Browser%20security.md)[Cryptographic protocols](https://jobicy.com/jobs?search_keywords=Cryptographic%20protocols.md)[WebPKI](https://jobicy.com/jobs?search_keywords=WebPKI.md)[Multithreaded programming](https://jobicy.com/jobs?search_keywords=Multithreaded%20programming.md)[Cross-platform development](https://jobicy.com/jobs?search_keywords=Cross-platform%20development.md)[Performance optimization](https://jobicy.com/jobs?search_keywords=Performance%20optimization.md)[Memory debugging](https://jobicy.com/jobs?search_keywords=Memory%20debugging.md)[HTML](https://jobicy.com/jobs?search_keywords=HTML.md)[CSS](https://jobicy.com/jobs?search_keywords=CSS.md)[JavaScript](https://jobicy.com/jobs?search_keywords=JavaScript.md) Sample interview questionsHow would you approach hardening a browser component that processes untrusted web content?I would first map assets, entry points, trust boundaries, privileges, and attacker capabilities. I would then prioritize isolation, least privilege, strict input validation, safe ownership and memory practices, and defense-in-depth controls, supported by threat modeling, targeted tests, fuzzing, and security review. Describe your process for diagnosing a memory or concurrency issue in a native multithreaded application. I begin by making the problem reproducible and collecting logs, crash data, and relevant traces. I use tools such as sanitizers, debuggers, profilers, and race detectors to narrow the fault, validate the root cause with a minimal reproduction, implement a safe fix, and add regression coverage. What considerations are important when changing a security-sensitive trust boundary? I would identify what data and capabilities cross the boundary, verify authentication and authorization assumptions, minimize exposed interfaces, and ensure failures default to a safe state. I would also evaluate compatibility and performance effects, involve relevant reviewers early, and test adversarial as well as normal flows. How would you evaluate a cryptographic protocol or WebPKI-related change in Firefox? I would confirm the relevant standards, existing browser behavior, threat model, and interoperability requirements. The implementation should use established cryptographic primitives and libraries, avoid custom crypto, handle invalid certificates and downgrade paths safely, and include comprehensive compatibility and negative-path testing. How do you communicate a complex security finding to engineers from different teams? I tailor the explanation to the audience while clearly stating the affected component, impact, exploitability, root cause, and recommended remediation. I provide actionable evidence and reproduction details to technical owners, document risk and trade-offs, and keep stakeholders updated through validation and deployment. Opportunity details ## About this role. 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 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 [hiringaccommodation@mozilla.com](mailto:hiringaccommodation@mozilla.com) 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 #LI-REMOTE Req ID: R3247 Hiring Ranges: Remote France €53.000—€71.000 EUR Show more [Apply now >](https://jobicy.com/jobs/157410-senior-software-engineer-firefox-security.md) * ![Upload CV](data:image/svg+xml;base64,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) ### Upload your resume now To unlock remote work opportunities and be discovered by global employers. 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