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Posted 28 d agoFirst seen 10 d ago
Senior Contract C++ / JavaScript Software Engineer (Browser Engine)
Posted by Mozilla on 22 September 2026, 28 days ago. Still on their Greenhouse board when we checked 3 min ago. Half of Mozilla's roles come down within 43 days.
What the posting is about
Improve Firefox's DOM Core and Session History area. Write tests, fix issues, and collaborate with module owners. Substantial experience in browser-engine codebases required.
Read out of the posting
LevelNot stated
Experience askedNot stated
EmploymentContract
LocationRemote Belgium, Remote Denmark, Remote Finland, Remote France, Remote Netherlands, Remote Poland
RemoteYes
Visa sponsorshipNot stated
SalaryNot published, and most postings do not
Posted2026-09-22
Found viagreenhouse, direct from their system
We saw it 18 days after it went up.
The posting, as the company wrote it
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.
Copied from Mozilla’s own board, not rewritten. Original ↗
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