Thunderbird Senior Software Engineer

Mozilla (View all Jobs)

Remote UK

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Interview Process

1. Deep-dive discussions on technical and mentorship problems solved in the past. No live coding. Total of 3 rounds.

Programming Languages Mentioned

C++, JavaScript

The Company

MZLA Technologies Corporation (MZLA) is a new, wholly owned subsidiary of Mozilla Foundation which runs the Thunderbird project. Thunderbird is a global, free, and open source email client that has grown significantly since its launch 10+ years ago! The project is governed by its community, which means that strategic and other high-level decisions are publicly discussed and decided upon by the elected Thunderbird Council. Thunderbird has grown in donations, staff, and aspirations over the last years. It is looking to mature and expand its business practices to ensure future operational success. This role is an opportunity for an experienced engineer who is excited to design and implement Thunderbird’s ongoing growth.

The Opportunity

The Thunderbird team is looking for a Senior JavaScript Engineer with some C++ knowledge to work on our full stack Calendar implementation as well as other areas of Thunderbird. You will help update our code base and craft new features for this already very popular cross-platform email client. We’re committed to creating an amazing experience for our users, and you’ll play a key part in this effort. You will be working with our existing staff and community members from all over the globe. We are key contributors to open source, allowing you to show your skills to the world both in terms of pure code and concrete product improvements. This is a remote, full time position. We expect excellent written communication skills so as to foster strong work coordination over email, video conferencing, Matrix, and Bugzilla.

What you’ll get to do:

  • Write code and tests, build prototypes, tackle problems with no clear solution, and collaborate with other designers and engineers as part of a global, distributed open source development team. This will involve technical decision making, code reviews (receiving and giving), engagement with contributors, planning and other collaborative development practices.
  • Help to build a comprehensive, threaded rework of the Thunderbird Calendar back-end from data storage to communication with calendar providers.
  • Debug and fix problems to improve the quality of our complex code base, making a better experience for tens of millions of users.
  • Since we’re a small team, you’ll have a major impact on the design and development of Thunderbird code and take ownership of the projects you work on.

We’re looking for someone with:

  • Excellent proficiency with JavaScript both with and without frameworks. 
  • 5+ years of experience developing with JavaScript/HTML/CSS and strong understanding of web technologies.
  • Knowledge of a systems programming language such as C, C++, or Rust.
  • Great communication skills (both written and verbal), documentation skills, and the ability to work with a multi-disciplinary, geographically distributed team.
  • Comfortable working on all levels of a complex software stack, as well as strong learning and exploration skills.
  • Deep respect for the different skills and perspectives that people of varied technical and non-technical backgrounds bring to a team.
  • Dedication to open source and open standards.
  • Proven ability to deliver and maintain complex software projects.
  • A passion for protecting users.

Bonus Points for:

  • Experience with native application development on Windows, Mac, iOS or Android.
  • Experience with application API design and foreign function interfaces.
  • Familiarity with add-ons or other previous open source engagement.
  • Experience with calendaring, scheduling, or time tracking systems and/or knowledge of related standards and specs.
  • French, German, Japanese, or any language proficiency in addition to English.
  • US, Canada - eastern time zone preferred.

We offer the following benefits:

  • 24 paid time off days per year (prorated) + your birthday
  • Company/public holidays + year-end shutdown
  • Remote work set-up - latest hardware + internet reimbursement
  • Health, dental, and vision insurance (employer-sponsored US; government programs in other locales)
  • Professional development opportunities
  • Other insurance (varies by geography)
  • Retirement plan contributions (US/Can only or as required by law)
  • Maternity and parental leaves (varies by geography)
  • Other legally required benefits (varies by geography)

Benefits are subject to change at any time at the discretion of MZLA Technologies Corp.

Applicants must reside in and have existing work authorization for the country location specified. We are unable to consider applicants outside of these locations and are unable to provide visa sponsorship.

MZLA Technologies Corporation (MZLA) Hiring Practices

Mozilla understands that valuing diverse creative practices and forms of knowledge are crucial to and enrich the company’s core mission. We encourage applications from everyone, including members of all equity-seeking communities, such as (but certainly not limited to) women, racialized and Indigenous persons, persons with disabilities, and persons of all sexual orientations and gender identities and expressions.

We are an equal opportunity employer and value diversity. We do not discriminate on the basis of race, religion, color, national origin, gender, sexual orientation, age, marital status, veteran status, or disability status.

We will ensure that individuals with disabilities are provided reasonable accommodation to participate in the job application or interview process, to perform essential job functions, and to receive other benefits and privileges of employment. Please contact us to request accommodation at

Group: C


Please mention No Whiteboard if you apply!
I'm a one-man team looking to improve tech interviews, and could use any support! 😄

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