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

Mozilla·Remote France·Remote·Posted 20 October 2026

Apply with a tailored CV View on Mozilla's site

About the role

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…

This is a summary of the advert. The full description and the application are on Mozilla's careers site.

Apply faster with Prepper

A version of your CV tailored to this Senior Contract C++ / JavaScript Software Engineer Firefox (Browser Engine) role.
A cover letter written from your CV and this advert.
Prepper can fill in Mozilla's application form and send it once you approve.
The application saved in your tracker, with reminders to follow up.

Start free

More roles at Mozilla

Prepper is independent and not affiliated with Mozilla. Roles are listed from the employer's public careers system and removed when they close.