Application Guide

How to Apply for Senior Software Engineer, Add-Ons

at Mozilla

🏢 About Mozilla

Mozilla is a non-profit-backed technology company that has championed an open, privacy-first internet for over 25 years, best known for Firefox. Unlike typical tech firms, it answers only to its mission—not shareholders—and serves 225+ million monthly users while exploring AI, security, and social media. Working here means contributing to open-source software that puts people before profit.

About This Role

As a Senior Software Engineer on the Add-Ons team, you’ll build and maintain addons.mozilla.org (AMO), the central hub where millions of users discover extensions and thousands of developers publish and manage them. You’ll work on the developer hub (DevHub), reviewer tools, and automated moderation systems that keep the ecosystem safe and thriving. This role directly impacts how Firefox users customize their browsing experience and how developers grow their add-ons.

💡 A Day in the Life

You might start your day with a async stand-up, then dive into code reviews for a new moderation feature or pair with a designer on DevHub UI improvements. Later, you could troubleshoot a performance issue on AMO, collaborate with the community on a bug report, or plan the next sprint with your distributed team. Expect a mix of hands-on coding, cross-functional collaboration, and mission-driven problem-solving.

🚀 Application Tools

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Interview Prep

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🎯 Who Mozilla Is Looking For

  • 5+ years of full-stack web development experience, with strong proficiency in JavaScript/TypeScript and modern frameworks (React, Node.js, or similar).
  • Proven track record building and scaling consumer-facing web platforms or marketplaces, ideally with open-source contributions.
  • Experience with developer tools, API design, and automated moderation or content review systems.
  • Comfortable working in a remote, async-first environment and collaborating with a global open-source community.
  • Passion for Mozilla’s mission of privacy, openness, and user empowerment on the web.

📝 Tips for Applying to Mozilla

1

Highlight any contributions to open-source projects, especially those related to Firefox, add-ons, or web standards—link to your GitHub or Bugzilla activity.

2

Tailor your resume to show experience with marketplace or developer-platform features (e.g., publishing workflows, review queues, API integrations).

3

In your cover letter, explicitly connect your work to Mozilla’s mission—mention how you’ve advanced privacy, openness, or user control in past roles.

4

If you’ve used Firefox add-ons or built one, describe that experience and any insights you gained about the ecosystem.

5

Mention familiarity with Mozilla’s tech stack (e.g., Django, React, MySQL, Elasticsearch) and tools like GitHub, Bugzilla, and Phabricator.

✉️ What to Emphasize in Your Cover Letter

Emphasize your hands-on experience building or maintaining developer platforms and marketplaces. Show how you’ve contributed to open-source communities and why Mozilla’s mission resonates with you. Highlight any work on moderation, review systems, or API design that directly relates to AMO. Finally, stress your ability to work remotely and asynchronously while collaborating with a distributed team.

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🔍 Research Before Applying

To stand out, make sure you've researched:

  • → Explore addons.mozilla.org as both a user and a developer—install a few add-ons, browse the DevHub, and review the submission guidelines.
  • → Read Mozilla’s mission statement and recent blog posts about their focus areas (AI, security, social media) to understand current priorities.
  • → Look into the technical architecture of AMO by reviewing public documentation, GitHub repositories, or engineering blog posts.
  • → Familiarize yourself with Mozilla’s Manifest V3 transition and any recent changes to the add-ons ecosystem.

💬 Prepare for These Interview Topics

Based on this role, you may be asked about:

1 How would you design a scalable system for reviewing and moderating thousands of add-on submissions daily?
2 Describe your experience with full-stack development and how you’ve optimized performance for a high-traffic web application.
3 What steps would you take to improve the developer experience on a platform like AMO’s DevHub?
4 How do you approach security and privacy when building features that handle user data and third-party code?
5 Give an example of a time you contributed to an open-source project and how you navigated community feedback.
Practice Interview Questions →

⚠️ Common Mistakes to Avoid

  • Submitting a generic resume that doesn’t highlight web platform or marketplace experience—Mozilla values specificity and mission alignment.
  • Neglecting to mention open-source contributions or community involvement, which are highly valued at Mozilla.
  • Focusing only on technical skills without demonstrating passion for Mozilla’s mission of privacy and an open internet.

📅 Application Timeline

This position is open until filled. However, we recommend applying as soon as possible as roles at mission-driven organizations tend to fill quickly.

Typical hiring timeline:

1

Application Review

1-2 weeks

2

Initial Screening

Phone call or written assessment

3

Interviews

1-2 rounds, usually virtual

✓

Offer

Congratulations!

Ready to Apply?

Good luck with your application to Mozilla!

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