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Mozilla

Contract Software Engineer - DOM Core Firefox/Gecko

MozillaΒ·11 days ago

πŸ“ ContractπŸ“ˆ Mid LevelπŸ‡¬πŸ‡§ UKπŸ“… Sep 22, 2026

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.

Market context

Measured from remote postings we have tracked ourselves β€” not self-reported survey data.

What Mid Level Engineering roles in Europe pay

25th
$65k
Median
$95k
75th
$135k

Based on 885 comparable postings with disclosed salaries, last 12 months.

How Mozilla is hiring

Last 90 days
146 roles
Total tracked
455
Hiring across
11 job families

Tracked since June 2025.

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