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Mozilla

Senior Contract Web Developer - Firefox (Browser Engine)

Remote Germany

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hirly's read of this role

Role family
Engineering
Seniority
Senior
Country
DE
Work mode
Remote-friendly
First seen by hirly
21 Oct 2026

Derived automatically from the posting. Upload your resume above to see how the role scores against it.

the posting

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.

Original posting on Mozilla's site ↗

Listed on hirly, a job board. hirly is not the employer: Mozilla is hiring for this role.

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