# Senior Contract C++ / JavaScript Software Engineer (Browser Engine) at Mozilla

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.

- Company: Mozilla
- Location: Remote Belgium; Remote Denmark; Remote Finland; Remote France; Remote Netherlands; Remote Poland
- Workplace: Remote
- Posted: 2026-09-22
- Apply: https://job-boards.greenhouse.io/mozilla/jobs/8223520
- Source: https://jobmagic.ai/jobs/senior-contract-c-javascript-software-engineer-browser-engine-mozilla-8dd25n

## Requirements

- 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.

## Description

### **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.