Principal Software Engineer, Developer Acceleration (Release Engineering)

We’re looking for a Staff Design Engineer to help shape the product experience for Thunderbolt as it moves from early product development into enterprise use cases. This role sits at the intersection of product design, front-end engineering, prototyping, and AI-assisted product development.

You’ll turn early product ideas, user needs, partner feedback, and workflow concepts into working prototypes and production-ready user experiences. This is not a role focused only on mockups or design artifacts. You’ll work directly in the codebase, use AI-assisted development tools thoughtfully, and help define the interaction patterns that make Thunderbolt intuitive, useful, trustworthy, and enterprise-ready.

You should be comfortable operating independently in ambiguity, moving quickly from concept to prototype, distinguishing between experiments and production-ready work, and creating reusable product and interaction patterns that help the broader team move faster.

What you’ll do

• Build functional prototypes and product experiments directly in the Thunderbolt codebase.
• Translate ambiguous product ideas, user workflows, partner feedback, and enterprise needs into clear, usable product experiences.
• Help define interaction patterns for AI-powered chat, search, research, workflow automation, knowledge retrieval, and enterprise administration.
• Use AI-assisted development tools to accelerate prototyping and implementation while maintaining strong judgment around quality, usability, security, accessibility, and maintainability.
• Partner closely with product, design, engineering, and enterprise-facing teams to explore, validate, and refine product direction.
• Contribute production-quality front-end code where appropriate.
• Identify when a prototype should be discarded, refined, generalized, or productionized.
• Improve the usability, accessibility, consistency, and polish of the Thunderbolt user experience.
• Help develop reusable components, interface patterns, or design-system elements that create leverage for the broader product team.
• Bring a user-centered perspective to technical and product discussions, especially where AI behavior, user trust, transparency, permissions, or workflow clarity are important.
• Consider enterprise needs when designing product experiences, including data sensitivity, user control, administrative visibility, auditability, and security expectations.
• Contribute to a product culture that values speed, clarity, experimentation, maintainability, responsible AI use, and thoughtful user experience.

• 10+ years of relevant experience in design engineering, front-end engineering, UX engineering, product design with strong technical implementation experience, or a closely related role, with demonstrated leadership and impact beyond individual deliverables.
• Strong front-end engineering skills, including experience with modern JavaScript or TypeScript, component-based frameworks, and building prototypes or production features directly in an application codebase.
• Strong product and interaction design judgment, including usability, accessibility, information architecture, workflow design, and product polish.
• Experience designing, prototyping, or building AI-enabled product experiences, such as chat, search, research tools, agents, automation, knowledge interfaces, or workflow tools where user trust, context, output quality, and human oversight are central to the experience.
• Experience translating ambiguous product concepts into usable workflows, prototypes, and shipped product experiences, with the judgment to balance speed, quality, maintainability, learning, and product risk.
• Experience providing technical or product leadership through mentoring, cross-functional coordination, reusable patterns, project ownership, or influence beyond individual deliverables.
• Practical awareness of AI, privacy, security, and regulatory considerations that may affect product experience, including transparency, user control, permissions, data handling, and trust; familiarity with frameworks such as the EU AI Act, Cyber Resilience Act, HIPAA, or comparable responsible AI, privacy, and security requirements.
• Strong communication and collaboration skills, including experience working closely with product managers, designers, engineers, and other cross-functional stakeholders.
• Portfolio, case studies, shipped work, or examples demonstrating design-to-code execution, interactive prototypes, or product experience improvements.

Bonus points for

• Experience with enterprise software, developer tools, productivity tools, collaboration tools, self-hosted software, or other technical user workflows.
• Experience contributing to design systems, component libraries, reusable front-end architecture, or shared product interaction patterns.
• Familiarity with user research, usability testing, product discovery, feature instrumentation, or rapid experimentation methods.
• Experience working in open-source or highly collaborative engineering environments., This is a remote, full-time position. Strong communication and documentation skills are essential for effective collaboration 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: $185,000 - $205,000 USD

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
• 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
• Year-end company shutdown
• 9 wellbeing days
• Public holidays
• Other paid leave
• Quarterly wellbeing stipend for personal / family activities

Health & family

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

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.

To learn more, visit www.thunderbird.net

The opportunity

Thunderbird is expanding beyond email with Thunderbolt, an open-source AI client designed for organizations that need more control over their data, infrastructure, and model choices., You’ll work with our passionate staff and open-source community members from all over the globe to support the mission and objectives of MZLA Technologies Corporation. In this role, you’ll also collaborate closely with engineering, product, design, enterprise-facing teams, contractors, and external contributors working on Thunderbolt.