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Senior Contract C++ / JavaScript Software Engineer Firefox (Browser Engine)

Mozilla Corporation • VPN & Proxy Services • Consumer & Utility Software • JavaScript • C++ • 3 days ago

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Salary

≈ $59k – $122k per year (Estimated)

Location

Remote (United Kingdom)also open in France, Germany

Seniority

Senior

Employment

Contractor

Confirmed on the employer's own hiring board on Oct 23, 2026. First seen by Alion on Oct 20, 2026. Mozilla Corporation scores A on the Alion truth index.

Overview

Company

Impact

Profile match

Mozilla Corporation

Mozilla Corporation is the commercial subsidiary of the non-profit Mozilla Foundation, created in 2005 to develop and distribute Firefox and related products. It is unusual in structure: profits flow back to the foundation rather than to shareholders, and the great majority of revenue has historically come from a single search default agreement, most recently with Google. Headquartered in Mountain View with a largely distributed workforce, it has been trying to reduce that dependence through advertising products, a virtual private network, the data removal service Monitor and its Anonym advertising measurement business.

mozilla.org • HQ: Mountain View, United States • VPN & Proxy Services • Consumer & Utility Software • 1001-5000 employees • Est. 2005

Tech stack of Mozilla Corporation

Backed by UpWest, Trinity Ventures, Yegor256

The role

You will help the Firefox DOM Core team improve the health of the Session History area. You will write tests to improve the coverage; you will fix tests and/or problems to improve the Gecko correctness.

Responsibilities

Write Web-Platform tests to improve the coverage, and Gecko mochitests as needed
Fix the problems and pass the tests to improve the Gecko correctness
Work through code review with the relevant Gecko module owners and iterate to landing

Definition of done

Improved Session History test coverage and code correctness in Gecko, measured by passed test cases, allowing the team’s senior engineers to focus on security, performance and strategic projects.

Required qualifications

Substantial experience in a browser-engine codebase or in automating for a browser-engine, ideally Firefox/Gecko.
Solid Javascript and applying that language skill to write automated tests.
Proficiency in and experience developing software in C++.
Strong debugging skills in a mature larget 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 web standards and Web Platform Tests.

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