Senior Mobile Engineer, iOS

Thunderbird is one of the world’s most trusted open-source email applications, empowering more than 20 million people globally. At MZLA, the team behind Thunderbird, we build privacy-respecting communication and productivity tools that help people manage their digital lives while staying in control of their data. We are open source by design, developing transparently and collaboratively with a global community of contributors. Our small but growing team of 60+ people is distributed across seven countries, working to evolve Thunderbird beyond a single desktop application into mobile, paid services, and new product experiences. Our revenue model combines user donations with paid services to ensure long-term sustainability and innovation.

A note about MZLA and Mozilla: MZLA Technologies Corporation is the nonprofit-owned company behind Thunderbird and part of the Mozilla family, with its own compensation programs, benefits, and employment policies.

About the role

The Senior Software Engineer, iOS is an experienced individual contributor who brings deep iOS expertise to the design, development, and evolution of Thunderbird’s iOS application. This role will help establish a strong technical foundation for the product, working closely with mobile engineers, product management, UX, and other partners to deliver a high-quality iOS experience. You’ll ensure the app meets high standards for performance, reliability, accessibility, security, and maintainability while aligning with MZLA’s mission and Thunderbird’s objectives. You’ll also collaborate with open-source contributors and mobile engineers across the broader Mozilla ecosystem.

Responsibilities

• Build and refine Thunderbird’s mobile products and platform architecture.
• Improve scalability, performance, reliability, and user experience.
• Develop a deep understanding of the codebase and architecture to confidently make changes across the entire stack.
• Maintain strong debugging and testing practices across unit, integration, and automated testing.
• Review code and guide improvements to architecture, testing, and development best practices.
• Independently resolve complex issues involving performance, security, and cross-platform integration.
• Monitor application health and address issues before they escalate.
• Document technical decisions, system architecture, and team processes.
• Own assigned projects, collaborating cross-functionally from investigation and planning through development, validation, and delivery.
• Ensure mobile development meets accessibility, security, and privacy standards.

Requirements

• 7+ years of professional software development experience, including 2+ years in a Senior Software Engineer role.
• 3+ years of professional mobile application development experience.
• Strong experience with Swift, SwiftUI, and iOS frameworks.
• Deep knowledge of iOS architecture, design patterns, and performance optimization.
• Experience delivering and maintaining complex, scalable, and reliable software.
• Experience addressing technical debt and refactoring large or complex codebases.
• Strong knowledge of mobile security, including encryption, secure storage, app signing, and vulnerability remediation.
• Experience with communication and email protocols such as RSS, IMAP, POP, or Matrix, and familiarity with IETF standards for CalDav or CardDav.
• Advanced proficiency with Git and collaborative development workflows.
• Strong debugging, testing, and problem-solving skills.
• Strong attention to detail, curiosity, and a product-focused mindset.
• Ability to work independently, take ownership, and collaborate across teams.
• Respect for diverse skills, experiences, and perspectives.
• Excellent async written communication skills; comfortable working with a geographically distributed team.
• Ability to learn, evaluate, and responsibly use emerging technologies, including AI-enabled tools, to improve work processes.

Nice to have

• Familiarity with Apple App Store and Google Play Store compliance guidelines.
• Experience contributing to open-source projects or communities.
• Proficiency in French, German, Japanese, or another widely supported Thunderbird language.

What success looks like

You’ll be successful in this role if you look beyond shipping features and focus on improving the architecture, reliability, security, and long-term health of the product. You’re comfortable solving ambiguous problems, flagging risks early, documenting decisions, and collaborating across engineering, product, UX, users, and the open-source community. Over time, your work will help Thunderbird’s iOS experience become more resilient, scalable, and easier for both staff and community contributors to build on.

Work environment

This is a full-time, fully remote position. You’ll join a distributed team of Thunderbird staff, open-source community members, and contributors from around the world. We rely on clear communication, thoughtful documentation, and collaborative decision-making to work effectively across time zones and disciplines.

Pay

We benchmark our base salaries to local markets and target the 60th percentile of the peer market. The salary ranges for this role are:

• US: $123,000 - $144,000 USD
• Canada: $108,000 - $125,000 CAD

We may consider candidates with strong skills but less than the required experience. Title, level, and compensation will be determined based on qualifications and experience.

Benefits

Work & career

• Fully remote work & schedule flexibility
• Company-provided laptop
• Annual bonus program
• Monthly remote work stipend
• Annual professional development stipend
• Access to Coursera learning platform
• Industry conferences
• Company all-hands and team gatherings

Rest & play

• 24 days PTO per year (prorated)
• Your birthday off
• Year-end company shutdown
• 9 wellbeing days
• Public holidays
• Other paid leave
• Quarterly wellbeing stipend for personal/family activities

Health & family

• 401(k) / RRSP contributions
• Health, dental, & vision insurance
• Disability insurance
• Life insurance
• Employee assistance program
• Paid parental leave
• Paid sick days

Applicants must reside in and have permanent work authorization for the country location(s) specified in the posting. We are unable to consider applicants outside of these markets at this time and do not provide visa sponsorship.