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The WebExtensions platform powers the add-ons ecosystem in Firefox, enabling millions of users to customize their browser while keeping safety and performance at the forefront. As a WebExtensions Engineer, you will help implement new extension capabilities, improve existing APIs, and ensure that extensions remain reliable across Firefox. As a Software Engineer on the WebExtensions team, you’ll bring a passion for exploring complex systems and creating experiences that balance developer power with user trust. You’ll work deep in the Gecko platform to evolve extension capabilities, and you’ll build UI features in Firefox that make extensions clear and manageable for users. Along the way, you’ll collaborate with experts across Mozilla and help advance cross-browser compatibility and the path toward standardization. Your work will keep extensions safe, powerful, and reliable for developers and millions of Firefox users.
Job Responsibility
Implement and maintain WebExtensions APIs and Addon Management, balancing power, safety, and performance, as well as user interfaces in Firefox
Debug and fix issues affecting extensions in Firefox
Collaborate with product managers, QA, and the AMO engineering team to deliver features end-to-end
Contribute to Mozilla-owned extensions and system add-ons
Participate in open source workflows: code reviews, pull requests, and discussions in Bugzilla/GitHub
Support extension developers by helping diagnose issues and improving tooling/documentation
Requirements
4+ years of professional experience in software development
Strong proficiency in JavaScript, DOM APIs, HTML, and CSS
Familiarity with modern browser architecture and debugging tools
Experience with API design and integration
Ability to navigate and learn from large codebases
Strong communication skills and experience collaborating in distributed teams
Nice to have
Experience with Firefox internals, C++ or Rust
Familiarity with Android or GeckoView development
Knowledge of web security principles
Contributions to open source projects, especially in browser or extension development
What we offer
Generous performance-based bonus plans to all eligible employees
Rich medical, dental, and vision coverage
Generous retirement contributions with 100% immediate vesting
Quarterly all-company wellness days
Country specific holidays plus a day off for your birthday