Senior Software Engineer, Firefox Desktop

About the role

Mozilla Corporation operates as the non-profit-backed technology company that has shaped the internet for the past 25 years, creating trusted products such as Firefox and advancing initiatives in AI, social media, security, and more. The Mozilla Corporation is wholly owned by the non-profit Mozilla Foundation, meaning it operates without shareholder influence and remains focused on its core mission to make the internet better for people. The Firefox team is a community of engineers dedicated to delivering a fast, friendly, and reliable browser, with Desktop Integrations focusing on updates, installs, and OS integration across platforms. This role is part of that team, contributing to OS integration, particularly on Windows and macOS, while working within a geographically distributed, open-source, and open-work environment.

This Senior Software Engineer role involves architecting and implementing core components of the Firefox desktop experience, with an emphasis on reliability and performance. You will own end-to-end delivery of features that span user-facing functionality and deep platform integration, directly influencing how hundreds of millions of users interact with their operating systems through the browser. The role requires autonomy to translate ambiguous requirements into technical solutions, mentoring junior engineers, and elevating team standards. Success in this position demands a balance of independent execution and seamless collaboration across a distributed global culture.

What you'll do

You will architect and maintain the installation and update pipelines that deliver Firefox to users worldwide, ensuring reliability and performance at scale. You will implement low-level integrations with Windows and macOS operating systems to support seamless browser functionality and diagnose complex performance and reliability metrics to guide improvements in the user installation experience. You will collaborate closely with product managers to translate high-level objectives into scoped technical deliverables, lead code reviews, and provide constructive feedback to maintain code quality. The role also involves diagnosing and resolving critical production incidents that impact Firefox deployments and partnering with cross-functional teams to align on goals and remove shipping blockers. You will champion software engineering best practices and contribute to defining technical standards for browser-OS interaction, owning debugging of intricate platform-specific issues that are difficult to reproduce in controlled environments.

You will contribute to the development and improvement of Firefox features related to installs, updates, and OS integrations. You will help implement enhancements to the Firefox installation and update experience, using data insights to guide development. You will tackle platform-specific challenges in low-level operating system integration on Windows and/or macOS. You will collaborate with your manager and teammates to scope and prioritize work in alignment with the team's goals. You will participate in code reviews and contribute to technical discussions with peers. You will take ownership of complex bugs and lead efforts to improve the Firefox experience for hundreds of millions of users. You will work closely with your geographically distributed team in a highly collaborative environment.

Requirements

You must bring 3-5 years of professional software engineering experience in a relevant field, with demonstrated proficiency in systems-level programming on at least one major platform such as Windows or macOS. You should have a strong understanding of operating system concepts, including file systems, processes, and inter-process communication, along with experience in native programming languages commonly used in desktop applications. The ability to read and interpret complex technical documentation and specifications is essential, and you must be capable of working effectively in a remote-first environment with a high degree of self-direction. Commitment to open-source principles and collaborative development workflows is required, as is strong written and verbal communication skills to articulate technical ideas to diverse audiences.

Nice to have

Contributions to open-source projects that demonstrate engineering excellence and collaboration are valued, as is experience with browser technologies or similar large-scale client applications.

Practical notes

This role is remote from France, with work conducted in a distributed and asynchronous manner. Travel is not expected as part of the core responsibilities. Visa requirements may apply depending on the candidate's location. Deadlines for applications are not specified and are reviewed on a rolling basis.