Senior Software Engineer, WebExtensions

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 Haves

• 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 You'll Be Doing

• 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

Perks and Benefits

• Generous performance-based bonus plans to all eligible employees - we share in our success as one team
• Rich medical, dental, and vision coverage
• Generous retirement contributions with 100% immediate vesting (regardless of whether you contribute)
• Quarterly all-company wellness days where everyone takes a pause together
• Country specific holidays plus a day off for your birthday
• One-time home office stipend
• Annual professional development budget
• Quarterly well-being stipend
• Considerable paid parental leave
• Employee referral bonus program
• Other benefits (life/AD&D, disability, EAP, etc. - varies by country)