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 • SwedenSenior💰 SEK 513,000 - SEK 684,000 per yearWebsite

Core Competencies

Role fit

Core Competencies

Use this summary to align your resume positioning with the role.

Demonstrates expertise in low-level software engineering with a strong focus on security features, cryptographic protocols, and performance optimization in multithreaded environments. Proficient in C and/or C++, with familiarity in web technologies and a collaborative approach to problem-solving across distributed teams.

Highest-signal resume keywords

Low-Level Software EngineeringC and/or C++ ProficiencySecurity FundamentalsMultithreaded Application DiagnosisWeb Technologies Familiarity

ATS Keywords

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Applicant Tracking System Keywords

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Hard Skills

C ProgrammingC++ ProgrammingSecurity MechanismsCryptographic ProtocolsWebPKIMemory OptimizationPerformance OptimizationMultithreadingCross-Platform DevelopmentRust

Soft Skills

Effective CommunicationCollaboration

Industry Keywords

Security PosturePrivilege IsolationTrust BoundariesSecurity-Sensitive Web APIsDistributed Teams

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
Contribute to and drive improvements to Firefox’s core security posture 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 addressing memory and performance challenges
Familiarity with web technologies (HTML, CSS, 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)