Sr. Staff Software Engineer, Browser (New Products)

Thunderbird

United States

Remote

CAD 255,000 - 341,000

Full time

9 days ago

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Benefits offered by this job

Performance-based bonus

Medical, dental, vision

retirement contributions

Home office stipend

Professional development budget

Well-being stipend

Parental leave

Employee referral bonus

Job summary

Mozilla Corporation is seeking a Sr. Staff Software Engineer for the New Products browser team. You will own engine-level investigations, implement experiments, and work across disciplines to improve browser internals.

The role emphasizes deep systems work, performance optimization, and collaboration with a leading engineering team on browser innovations. Remote-friendly, US and Canada locations supported.

Qualifications

Deep hands-on expertise in at least one browser engine subsystem (e.g., DOM/Web APIs, layout, rendering, JS runtimes)
Strong proficiency in C++ or Rust with experience in large systems codebases
Ability to design prototypes and interpret results with reproducible evidence
Understanding of web platform behavior and compatibility in complex browser scenarios
Experience profiling, tracing, tests, or conformance checks with data-backed claims

Responsibilities

Design and implement experiments within browser engine subsystems.
Evaluate representations of browser state for accuracy and performance.
Prototype engine capabilities to support programmatic interaction with web content.
Instrument browser behavior and measure performance, documenting results clearly.
Profile overhead of new capabilities and explore AI-assisted tooling with rigorous validation.

Skills

Browser engine subsystem

C++

Rust

Memory ownership

Concurrency

Performance debugging

Prototype/experimentation

Web platform understanding

Profiling and tests

AI tool usage

Tools

JavaScript tooling

Job description

Sr. Staff Software Engineer, Browser (New Products)

at Mozilla Corporation

Team: New Products

Locations: Remote US, Remote Canada

About This Team And Role

Mozilla is seeking experienced browser engineers to join a small team exploring new applications of browser technology. The work combines deep systems engineering, rapid experimentation, and close collaboration across technical disciplines.

We are looking for a browser engine specialist who enjoys turning difficult systems questions into working experiments. You will investigate browser behavior, implement changes deep in the engine, and establish which ideas produce meaningful improvements. This is a hands‑on individual contributor role with ownership of engine‑level investigations and implementation, working closely with the team’s technical lead.

The work suits someone who has built or substantially changed browser internals, understands the tradeoffs embedded in those systems, and enjoys applying that knowledge to unfamiliar problems. Your experiments will help inform technical direction.

What You'll Do

Design and implement experiments within browser engine subsystems. Investigate how internal data structures and execution behavior affect performance, correctness, and the interfaces exposed to developer tools.
Evaluate ways to represent and expose browser state efficiently and accurately. Identify the tradeoffs in each approach, including information loss, implementation complexity, and compatibility with dynamic web content.
Prototype engine capabilities that support reliable programmatic interaction with web content. Investigate how document structure, layout, navigation, and event handling affect correctness and performance.
Instrument browser behavior and evaluate changes against repeatable tasks. Measure performance and correctness, isolate the effect of each change, and document unsuccessful experiments as clearly as successful ones. Check that gains hold beyond the workloads used to develop the prototype.
Profile the overhead introduced by new capabilities and pursue improvements where measurements justify them. Use AI tools to accelerate coding and analysis, and verify their output through debugging, tests, and measurement.

What You'll Bring

Deep hands‑on expertise in at least one browser engine subsystem, such as DOM and Web APIs, layout and rendering, accessibility, JavaScript runtimes, or networking and process architecture. You have implemented substantial changes and can trace their effects into neighboring subsystems.
Strong proficiency in C++ or Rust, experience navigating a large systems codebase, and practical knowledge of memory ownership, concurrency, object lifetimes, and performance debugging. You can build the JavaScript and scripting tools needed to exercise and measure your work.
A demonstrated ability to investigate unfamiliar code, form a precise hypothesis, construct a useful prototype, and interpret the results. You can separate the effects of your implementation from variability in websites, workloads, or model behavior.
A strong understanding of web platform behavior and compatibility. You can reason about how document structure, script execution, rendering, and user interaction relate, including cases where the browser’s internal state is difficult to expose accurately to another system.
Experience with profiling, tracing, regression tests, or conformance tests, and a habit of grounding performance claims in reproducible evidence. You can explain both the benefit of an optimization and the circumstances in which it fails.
Curiosity about AI agents and a willingness to work directly with agent harnesses and coding tools. You can connect a low-level implementation choice to the information an agent receives and the work it must do next.

Nice To Have

Contributions to Gecko, Servo, Blink, WebKit, or another browser engine
Experience maintaining an open‑source project
Technical leadership in a small team building a new product
Experience with accessibility infrastructure, browser security, profiling, or automated evaluation of agent workflows

What You’ll Get

Generous performance-based bonus plans to all eligible employees – we share in our success as one team
Rich medical, dental, and vision coverage
Generous retirement contributions with 100% immediate vesting (regardless of whether you contribute)
Quarterly all-company wellness days where everyone takes a pause together
Country specific holidays plus a day off for your birthday
One-time home office stipend
Annual professional development budget
Quarterly well-being stipend
Considerable paid parental leave
Employee referral bonus program
Other benefits (life/AD&D, disability, EAP, etc. – varies by country)

About Mozilla

Mozilla exists to build the Internet as a public resource accessible to all because we believe that open and free is better than closed and controlled. When you work at Mozilla, you give yourself a chance to make a difference in the lives of Web users everywhere. And you give us a chance to make a difference in your life every single day. Join us to work on the Web as the platform and help create more opportunity and innovation for everyone online.

Commitment to diversity, equity, inclusion, and belonging

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, persons of all sexual orientations, gender identities, and expressions.

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 hiringaccommodation@mozilla.com to request accommodation.

We are an equal opportunity employer. We do not discriminate on the basis of race (including hairstyle and texture), religion (including religious grooming and dress practices), gender, gender identity, gender expression, color, national origin, pregnancy, ancestry, domestic partner status, disability, sexual orientation, age, genetic predisposition, medical condition, marital status, citizenship status, military or veteran status, or any other basis covered by applicable laws. Mozilla will not tolerate discrimination or harassment based on any of these characteristics or any other unlawful behavior, conduct, or purpose.

Hiring Ranges

US Tier 1 Locations