Senior Software Engineer, WebExtensions

Software Engineer – WebExtensions

Join Mozilla and help shape the future of the open internet. As the organization behind Firefox and other privacy-focused technologies, Mozilla has spent more than 25 years building products that put people first. Today, millions of users worldwide rely on Mozilla products, and we’re continuing to innovate across areas including browser technology, AI, privacy, security, and the open web.

Unlike traditional technology companies, Mozilla is wholly owned by the non-profit Mozilla Foundation, allowing us to focus on our mission rather than shareholders. Our goal is simple: build a better internet that remains open, accessible, and beneficial for everyone.

About the Team

The WebExtensions Team powers Firefox’s add-on ecosystem, enabling millions of users to customize their browser experience while maintaining high standards of safety, privacy, and performance.

As a Software Engineer – WebExtensions, you will help develop and maintain extension capabilities within Firefox, improve extension APIs, contribute to browser architecture, and create intuitive user experiences for extension management.

You will collaborate closely with engineers, product managers, QA teams, and open-source contributors to ensure Firefox extensions remain powerful, reliable, and secure.

What You’ll Do

• Design, implement, and maintain WebExtensions APIs and Add-on Management features.
• Develop Firefox user interfaces that improve extension discovery, management, and usability.
• Balance functionality, security, performance, and user trust when building browser capabilities.
• Investigate, debug, and resolve issues affecting Firefox extensions.
• Collaborate with Product Management, Quality Assurance, and the Add-ons Engineering Team to deliver features end-to-end.
• Contribute to Mozilla-owned browser extensions and system add-ons.
• Participate in open-source development workflows, including:
  • Code reviews
  • Pull requests
  • Technical discussions
  • Bug tracking and resolution
• Support extension developers by helping diagnose technical issues and improve documentation and tooling.
• Collaborate with internal and external stakeholders to advance browser compatibility and web standards.

What We’re Looking For

• 4+ years of professional software engineering experience.
• Strong proficiency in:
  • JavaScript
  • HTML
  • CSS
  • DOM APIs
• Experience working with API design and integrations.
• Solid understanding of modern browser architecture and debugging tools.
• Ability to work effectively within large and complex codebases.
• Strong analytical and problem-solving skills.
• Excellent written and verbal communication skills.
• Experience collaborating within distributed or remote engineering teams.

Preferred Qualifications

• Experience working with Firefox internals.
• Knowledge of:
  • C++
  • Rust
• Experience with Android development or GeckoView.
• Understanding of modern web security principles.
• Contributions to open-source projects.
• Experience with browser, extension, or platform development.

What We Offer

Performance & Financial Rewards

• Performance-based bonus programs for eligible employees.
• Opportunity to share in company-wide success.
• Generous retirement contributions with immediate vesting.

Health & Wellbeing

• Comprehensive medical, dental, and vision coverage.
• Quarterly wellness days dedicated to employee wellbeing.
• Quarterly wellbeing stipend.
• Employee Assistance Program (EAP) and additional wellness benefits.

Time Off & Flexibility

• Country-specific public holidays.
• Additional day off for your birthday.
• Generous paid parental leave.

Professional Growth

• Annual professional development budget.
• Opportunities to learn from industry experts and contribute to impactful open-source projects.

Remote Work Support

• One-time home office stipend.
• Resources and tools to support productive remote work.

Additional Benefits

• Employee referral bonus program.
• Life insurance, disability coverage, and additional country-specific benefits.

Why Join Mozilla?

• Work on products used by millions of people around the world.
• Help build a more open, private, and accessible internet.
• Contribute to one of the world’s largest open-source communities.
• Collaborate with talented engineers, researchers, and contributors across the globe.
• Make a meaningful impact on the future of the web.

Our Mission

Mozilla exists to ensure that the internet remains a public resource that is open and accessible to everyone. We believe that openness, transparency, and innovation create better outcomes for users and society.

By joining Mozilla, you will have the opportunity to contribute to technologies that empower people online while advancing a mission-driven approach to software development.

Diversity, Equity, Inclusion & Belonging

Mozilla is committed to fostering an inclusive workplace where diverse perspectives, experiences, and backgrounds are valued. We encourage applications from individuals of all identities, communities, and lived experiences.

• Equal opportunity employer.
• Inclusive and accessible hiring practices.
• Reasonable accommodations available throughout the recruitment process.
• Commitment to creating a respectful, welcoming, and discrimination-free workplace.

We celebrate diversity and believe it strengthens our mission, our products, and our community.

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