About the role
Senior Contract C++ / JavaScript Software Engineer (Browser Engine) at Mozilla in Remote Belgium; Remote Denmark; Remote Finland; Remote France; Remote Netherlands; Remote Poland. Remote. Posted September 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.
Prefer to apply yourself? Apply on Mozilla’s site
Quick answers
Is this job remote?
Yes, this is a remote role for candidates in BE.
How do you apply?
Apply on Mozilla’s site using the link on this page. With a free Jobmagic account you can see how well you fit first.
Similar jobs
Senior Counsel, AI Product
OpenAI · Washington, DC · San Francisco · Hybrid
$330k–$366k · 10 hours ago
Staff Analytics Engineer
Coinbase · Remote
10 hours ago
Manufacturing Quality Engineer, Data Center Equipment
OpenAI · US - Remote · Hybrid
$165k–$290k · 10 hours ago