Senior Mobile Engineer, iOS

Mozilla Corporation; Northern (KY); On-site; USD 123,000 - 144,000; Full time

Benefits offered by this job

Fully remote work

Company laptop

Monthly remote work stipend

Learning stipend (Coursera)

Industry conferences access

Wellbeing and family benefits

Job summary

MZLA Technologies Corporation, the nonprofit-owned company behind Thunderbird, is seeking a Senior Software Engineer for iOS. You will contribute to Thunderbird’s iOS app, collaborating with mobile engineers, product, UX, and the open-source community to deliver a high-quality iOS experience with strong performance, accessibility, and security.

You will work across the stack to improve reliability and maintainability, while translating product needs into robust technical solutions and aligning

Qualifications

• 7+ years of professional software development experience.
• 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.
• Proficiency in email protocols such as RSS, IMAP, POP, or Matrix; familiarity with CalDav/CardDav standards.
• Advanced proficiency with Git and collaborative development workflows.
• Excellent async written communication; ability to work with distributed teams.
• Ability to learn and apply emerging technologies including AI-enabled tools.
• Experience contributing to open-source projects or communities.

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 to confidently modify the entire stack.
• Maintain strong debugging and testing practices across unit, integration, and automated tests.
• Review code and guide improvements to architecture, testing, and development practices.
• Independently resolve complex issues involving performance, security, and cross-platform integration.
• Monitor application health and address issues proactively.
• Document technical decisions, system architecture, and team processes.
• Own assigned projects from investigation and planning through development and delivery.
• Ensure mobile development meets accessibility, security, and privacy standards.

Skills

Swift

SwiftUI

iOS frameworks

Architecture

Performance optimization

Security

Git

Debugging & testing

Open-source collaboration

Tools

Git

Job description

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. Our products are developed transparently and in collaboration with a global community of contributors, and that same spirit shapes how we work: collaboratively, inclusively, and with a shared commitment to putting users first.

We are a small but growing company of 60+ people distributed across seven countries. As Thunderbird evolves beyond a single desktop application, we are expanding across desktop, mobile, paid services, and new product experiences that help people and organizations work more effectively without giving up control to big tech ecosystems.

Our revenue model combines user donations, which help keep Thunderbird’s apps freely available, with paid services that cover the costs of hosted offerings while supporting long-term sustainability and continued innovation.

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

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 continue to contribute to Thunderbirds effort to develop the iOS app and establish a strong technical foundation for the product.

You’ll work closely with mobile engineers, product management, UX, and other partners to deliver a high-quality iOS experience that meets high standards for performance, reliability, accessibility, security, and maintainability.

You’ll play an important role in delivering exceptional user experiences for Thunderbird’s global user base by translating product needs into thoughtful technical solutions and ensuring your work aligns with MZLA’s mission and the objectives of the Thunderbird Project. You’ll also collaborate with open-source contributors and mobile engineers across the broader Mozilla ecosystem.

What you’ll do

• 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 escalated.
• 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.

What you bring

• 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 the 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.
• The 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.
• 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 improve 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.

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.

In addition to competitive salaries, we offer a comprehensive benefits package designed to support your whole self.

Work & career

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

Rest & play

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

Health & family

• 401(k) / RRSP contributions
• Disability insurance
• Life insurance
• Employee assistance program
• Paid parental leave

Work eligibility

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, we do not provide visa sponsorship.

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