---
title: "Contract Software Engineer - DOM Core Firefox/Gecko"
company: "Mozilla"
company_url: "https://www.remjobs.works/companies/mozilla"
url: "https://www.remjobs.works/job/mozilla-contract-software-engineer-dom-core-firefox-gecko-77166f32-2e3c-4a1c-8fe4-fe56152f7aef"
apply_url: "https://job-boards.greenhouse.io/mozilla/jobs/8223520"
workplace: remote
location: "Remote France; Remote Germany; Remote UK"
remote_scope: "France; Germany; UK"
employment_type: unspecified
seniority: mid
role: software-engineering
region: united-kingdom
skills: ["cpp", "javascript"]
date_posted: 2026-09-22T15:43:45.000Z
first_seen_by_remjobs: 2026-09-22T16:19:52.040Z
---

# Contract Software Engineer - DOM Core Firefox/Gecko

**Mozilla** · Remote France; Remote Germany; Remote UK

Apply: https://job-boards.greenhouse.io/mozilla/jobs/8223520

## About Mozilla

Mozilla is the not-for-profit behind the lightning fast Firefox browser. We put people over profit to give everyone more power online.

## About the role

#### 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.

---

Source: Mozilla's own career page, read by RemJobs. Canonical HTML version: https://www.remjobs.works/job/mozilla-contract-software-engineer-dom-core-firefox-gecko-77166f32-2e3c-4a1c-8fe4-fe56152f7aef