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Mozilla

Contract Software Engineer – DOM Core, Firefox/Gecko

Mozilla

. Improve the health of the Firefox DOM Core team’s Session History area .

Posted 9/22/2026contractRemote • France, Germany, United KingdomMid-LevelSeniorWebsite

Core Competencies

Role fit
Core Competencies

Use this summary to align your resume positioning with the role.

Demonstrates expertise in improving browser-engine codebases, particularly in enhancing test coverage and code correctness for Firefox/Gecko. Proficient in writing automated tests using JavaScript and C++, with strong debugging capabilities in large codebases.

Highest-signal resume keywords
Browser-Engine Codebase ExperienceJavaScript Automated TestingC++ Software DevelopmentDebugging SkillsWeb Standards Familiarity

ATS Keywords

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Applicant Tracking System Keywords

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Hard Skills
JavaScriptC++Automated TestingDebuggingCode ReviewGeckoWeb Platform TestsSession History ImprovementTest CoverageMochitests
Soft Skills
CollaborationComfort Working in the Open
Industry Keywords
FirefoxGeckoBrowser EnginePublic BugsUpstream Landing

Tech Stack

Tools & technologies
JavaScriptC++

About the role

Key responsibilities & impact
  • Improve the health of the Firefox DOM Core team’s Session History area
  • Write Web-Platform tests to improve coverage and Gecko mochitests as needed
  • Fix problems and pass tests to improve Gecko correctness
  • Work through code review with relevant Gecko module owners and iterate to landing
  • Deliver improved Session History test coverage and Gecko code correctness, measured by passed test cases

Requirements

What you’ll need
  • Substantial experience in a browser-engine codebase or in automating for a browser-engine, ideally Firefox/Gecko
  • Solid Javascript skills applied to writing automated tests
  • Proficiency in and experience developing software in C++
  • Strong debugging skills in a mature large codebase
  • Comfort working in the open: public bugs, code review, and upstream landing
  • Prior contributions to Gecko or another major browser engine (preferred)
  • Familiarity with web standards and Web Platform Tests (preferred)

Benefits

Comp & perks
  • Contract position
  • Remote work in France, Germany, or the UK