# Senior Contract Software Engineer (JavaScript) - Firefox 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-software-engineer-javascript-firefox-at-mozilla-2699
Last updated: 2026-10-28

| | |
| --- | --- |
| Company | Mozilla |
| Location | 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-software-engineer-javascript-firefox-at-mozilla-2699) 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.*

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