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Mozilla

Contract Staff Software Engineer – (Firefox) C++,Storage Encryption

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Remote from
UK, Canada, Germany
Salary
Undisclosed
Department
Software Engineering
Employment
Contract
Experience
Senior
Published
Apply before
20 Nov 2026
Listing views
34
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AI Summary

The role, at a glance.

Mozilla is seeking a contract Staff Software Engineer to help deliver Storage Encryption Everywhere in the Firefox Gecko browser engine. The work includes schema migration, private-browsing storage implementation, integration testing, Web Platform Tests, and Gecko-specific tests. The engineer will collaborate through public issue tracking and code review, resolve standards questions, and shepherd the feature through Firefox Nightly, Beta, and Release channels. This is a senior systems-focused role requiring strong C++, database expertise, multithreaded debugging, and substantial browser-engine experience. The role is explicitly remote for candidates in Canada, Germany, or the UK.

Role DNA

A quick view of the complexity, pace, ownership and collaboration implied by the job description.

Job Complexity

5/5
EasyHard

Pace & Pressure

4/5
RelaxedFast-paced

Autonomy Level

5/5
GuidedFull ownership

Communication Load

4/5
IndependentCollaborative
AI insightThe role requires staff-level ownership of a security-sensitive browser-storage feature in a large, multithreaded C++ codebase. Success depends on navigating Gecko architecture, web standards, release channels, performance regressions, and upstream review processes independently.

Salary analysis

Estimated compensation compared with the broader US market for similar roles.

Estimated job median (per year)Market rate
$160,000
US market range (per year)$140k–$210k
AI insightThe yearly pay period is inferred from the job context; it was not explicitly stated by the employer. No employer compensation was disclosed. The yearly cadence is inferred from the senior full-time-equivalent software-engineering role and common market practice; estimated annual USD market compensation is $140,000–$210,000, with an estimated midpoint of $160,000.

Core skills

Skills and capabilities most closely associated with this opportunity.

C++Firefox GeckoBrowser enginesStorage encryptionDatabase systemsSchema migrationPrivate Browsing ModeWeb Platform TestsIntegration testingMultithreaded debuggingPerformance optimizationCode reviewWeb standardsRelease engineering
Sample interview questions
How would you approach implementing encrypted storage while preserving compatibility with existing user data?

I would first map the current storage formats, access paths, and migration constraints. I would design an incremental, recoverable migration with versioning, transactional safeguards, rollback behavior where possible, and tests covering upgrades, interruption, corruption, and private-browsing boundaries.

Describe your experience debugging a race condition in a multithreaded C++ system.

I begin by making the failure reproducible with targeted logging, assertions, and stress testing. I then trace ownership, thread affinity, locking, and lifetime assumptions, use sanitizers or race-detection tooling where available, and fix the underlying synchronization or design issue before adding a regression test.

How would you validate a new Firefox storage behavior against web standards?

I would identify the relevant specification requirements and translate them into observable browser behavior. I would add or update Web Platform Tests for interoperable requirements, create Gecko-specific tests for internal behavior, and use test results and specification discussion to resolve ambiguities.

What is your process for handling a performance regression introduced by a security feature?

I would establish a baseline, isolate the regression with profiling and representative workloads, and determine whether the cost comes from I/O, encryption, locking, allocation, or cache behavior. I would evaluate safe alternatives, validate the fix with benchmarks and correctness tests, and monitor behavior through the release pipeline.

How do you work effectively in an open-source code-review environment with module owners?

I prepare small, well-scoped patches with clear rationale, tests, and documentation of trade-offs. I respond constructively to review feedback, incorporate module-owner guidance, keep public issue discussions current, and escalate specification or architectural questions early when they affect implementation decisions.

This analysis is generated from the job description. Salary estimates, role characteristics and sample answers are guidance, not employer-provided facts.
Opportunity details

About this role.

The role

You will help the Firefox DOM LWS team to implement tasks for Storage Encryption everywhere, helping to drive the in-progress project through to completion .

Responsibilities

  • Contributing to delivering Storage Encryption Everywhere in Gecko, which may include tasks such as migrating data between schemas, implementing data storage in PBM and integration testing.
  • Write and pass Web Platform Tests, and add Gecko tests as needed.
  • Work through code review with the relevant Gecko module owners and iterate to landing.
  • Surface and help resolve any specification questions the implementation raises.
  • Shepherd the feature through Nightly, Beta, and Release. Fix correctness, performance issues and regressions.

Definition of done

Ship Storage Encryption Everywhere to release channel. Fix triaged and prioritized issues.

Required qualifications

  • Strong C++.
  • Substantial experience in a browser-engine codebase, ideally Firefox/Gecko.
  • Substantial experience in databases.
  • Familiarity with web standards and Web Platform Tests.
  • Strong debugging and optimization in a multithreaded codebase.
  • Comfort working in the open: public bugs, code review, and upstream landing.

Preferred

  • Prior contributions to Gecko or another major browser engine.
  • Familiarity with the relevant standards body and specification process.

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