Senior Software Engineer, Firefox Security

Mozilla

. Design, implement, test, and ship security and hardening features that strengthen Firefox’s security posture for enterprise users .

Posted 10/15/2026full-timeRemote • FranceSenior💰 €53,000 - €71,000 per yearWebsite

Core Competencies

Role fit

Core Competencies

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Demonstrates expertise in low-level software engineering with a strong focus on security features and mechanisms. Proficient in diagnosing and resolving issues in multithreaded, cross-platform applications while effectively communicating technical concepts.

Highest-signal resume keywords

C ProgrammingC++ ProgrammingSecurity FundamentalsMultithreaded Application DevelopmentWeb Technologies

ATS Keywords

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Applicant Tracking System Keywords

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Hard Skills

Low-Level Software EngineeringCryptographic ProtocolsWebPKISecurity-Sensitive Web APIsMemory ManagementPerformance OptimizationRust Programming

Soft Skills

Effective CommunicationTeam Collaboration

Tools & Technologies

FirefoxCross-Platform Development

Industry Keywords

Security ArchitecturePrivilege IsolationTrust BoundariesRoot Cause Analysis

Tech Stack

Tools & technologies

JavaScriptRustC++

About the role

Key responsibilities & impact

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

Requirements

What you’ll need

3+ years of experience in low-level software engineering
Strong proficiency in C and/or C++
Solid understanding of security fundamentals
Experience diagnosing and resolving issues in multithreaded, cross-platform native applications
Experience with memory and performance challenges
Familiarity with web technologies: HTML, CSS, and JavaScript
Interest or experience in Rust
Ability to work effectively within large, complex, multi-language codebases
Experience working with distributed teams
Ability to communicate technical ideas clearly in writing and conversation

Benefits

Comp & perks

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)