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

> 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 te...

Canonical: https://gigoranetwork.com/remote-jobs/senior-contract-c-javascript-software-engineer-firefox-browser-en-at-mozilla-2700
Last updated: 2026-10-27

| | |
| --- | --- |
| Company | Mozilla |
| Location | Remote France; Remote UK |
| Open to | Europe |
| Type | Contract |
| Category | Engineering |
| Level | Senior |
| Posted | 2026-10-20 |

## How to apply

Applications go through Mozilla's own careers site. Open the job page (https://gigoranetwork.com/remote-jobs/senior-contract-c-javascript-software-engineer-firefox-browser-en-at-mozilla-2700) and choose Apply; GigoraNetwork then keeps track of the application for you.

## Job 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.

*Description written by Mozilla and listed from its public job board.*

## Related

- [Senior Account Executive at Mozilla](https://gigoranetwork.com/remote-jobs/senior-account-executive-at-mozilla-3860)
- [Senior Account Executive at Mozilla](https://gigoranetwork.com/remote-jobs/senior-account-executive-at-mozilla-3861)
- [Contract Sr Data Analyst (SQL,Telemetry,Browser Engine) at Mozilla](https://gigoranetwork.com/remote-jobs/contract-sr-data-analyst-sqltelemetrybrowser-engine-at-mozilla-3825)
- [Contract Senior Data Analyst (SQL,Telemetry,Browser Engine) at Mozilla](https://gigoranetwork.com/remote-jobs/contract-senior-data-analyst-sqltelemetrybrowser-engine-at-mozilla-3824)
- [Staff Site Reliability Engineer, Tools & Systems at Mozilla](https://gigoranetwork.com/remote-jobs/staff-site-reliability-engineer-tools-systems-at-mozilla-3694)
- [Senior Professional Services Engineer - PubSec at GitLab](https://gigoranetwork.com/remote-jobs/senior-professional-services-engineer-pubsec-at-gitlab-3896)
- [Senior Solutions Architect at GitLab](https://gigoranetwork.com/remote-jobs/senior-solutions-architect-at-gitlab-3897)
- [Solutions Engineer | PST or EST US | Remote at Grafana Labs](https://gigoranetwork.com/remote-jobs/solutions-engineer-pst-or-est-us-remote-at-grafana-labs-3898)
- [Senior Software Engineer, Certificates Management at Coinbase](https://gigoranetwork.com/remote-jobs/senior-software-engineer-certificates-management-at-coinbase-3889)
- [Mobile Engineer - ElevenMusic at ElevenLabs](https://gigoranetwork.com/remote-jobs/mobile-engineer-elevenmusic-at-elevenlabs-1137)
- [iOS Engineer - Creative App at ElevenLabs](https://gigoranetwork.com/remote-jobs/ios-engineer-creative-app-at-elevenlabs-3643)