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Senior Contract Software Engineer (JavaScript) - Firefox

MozillaUKContractSalary not listed · Typical pay in United KingdomPosted Oct 29, 2026
Job description

About the role

Full text from the employer, as published on Jobicy, arranged into sections. Nothing added or removed.

01The 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.

02Responsibilities

  • 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

03Definition 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.

04Required 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.

05Preferred

  • Prior contributions to Gecko or another major browser engine.
  • Familiarity with web standards and Web Platform Tests.
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DGJ Insight

Our own data about this role and place, from official statistics and our live job index.

Updated Oct 30, 2026
Pay benchmark
Average wage, United Kingdom
GBP 46,511 average / year

Source: OECD Average annual wages, 2025

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