Senior Platform Engineer, WebExtensions

• Work deep in the Gecko platform to implement and maintain WebExtensions APIs and Addon Management, balancing developer power, user safety, and performance. • Build and maintain user interfaces in Firefox that make extensions clear and manageable for millions of users. • Collaborate with experts across Mozilla, product managers, QA, and the AMO engineering team to deliver features end-to-end. • Contribute to cross-browser compatibility efforts and help advance WebExtensions standardisation across the web platform. • Work fully remotely from the UK, France, Germany, or Canada.

• Bring 4+ years of professional software development experience. • Bring strong proficiency in JavaScript, DOM APIs, HTML, and CSS. • Bring familiarity with modern browser architecture and debugging tools. • Bring experience with API design and integration. • Show the ability to navigate and learn from large, complex codebases and collaborate effectively in distributed, open source teams.

• Bring experience with Firefox internals, C++, or Rust. • Bring familiarity with Android or GeckoView development. • Bring knowledge of web security principles. • Bring a history of contributions to open source projects, especially in browser or extension development.

• Implement and maintain WebExtensions APIs and Addon Management, keeping extensions safe, powerful, and reliable for developers and users. • Debug and fix issues affecting extensions in Firefox across platforms. • Participate in open source workflows including code reviews, pull requests, and discussions in Bugzilla and GitHub. • Support extension developers by diagnosing issues and improving tooling and documentation. • Contribute to Mozilla-owned extensions and system add-ons as part of a collaborative, distributed engineering team.

• Receive generous performance-based bonus plans shared across the team. • Access rich medical, dental, and vision coverage, plus generous retirement contributions with 100% immediate vesting. • Take considerable paid parental leave and a day off for your birthday, plus quarterly all-company wellness days. • Receive a one-time home office stipend, an annual professional development budget, and a quarterly wellbeing stipend. • Benefit from an employee referral bonus programme and additional benefits including life, AD&D, disability, and EAP cover.

Mozilla Corporation is the non-profit-backed technology company behind Firefox, used by more than 225 million people monthly. Wholly owned by the Mozilla Foundation, Mozilla builds open-source software that enables people to enjoy the internet on their own terms — never beholden to shareholders, always focused on making the internet better for people.