Senior Staff Software Engineer (Browser, New Products)

Mozilla; Ottawa; On-site; CAD 120,000 - 160,000; Full time

Benefits offered by this job

Health and wellness

Mental health

Time away

Parental leave

Learning and development

Life insurance

Wellbeing stipend

Employee referral bonus

Internet reimbursement

Office budget

Job summary

Mozilla is seeking experienced browser engineers to join a small team exploring new applications of browser technology. The role focuses on engine‑level investigations, experimental prototypes, and close collaboration with technical leadership to drive measurable improvements across browser subsystems.

The candidate will own hands‑on investigations, implement changes deep in the engine, and assess performance, correctness, and compatibility with dynamic content.

Qualifications

• Deep hands-on expertise in at least one browser engine subsystem (e.g., DOM/Web APIs, layout, rendering).
• Strong proficiency in C++ or Rust and memory ownership concepts.
• Experience with profiling, tracing, regression tests, or conformance tests.
• Experience maintaining an open‑source project and technical leadership in a small team.
• Interest in accessibility, browser security, and automated evaluation of agent workflows.

Responsibilities

• Design and implement experiments within browser engine subsystems.
• Investigate performance, correctness, and interfaces exposed to developer tools.
• Prototype engine capabilities for reliable programmatic interaction with web content.
• Instrument browser behavior, measure changes, and document outcomes clearly.
• Use AI tools to accelerate coding and analysis, validated by tests and measurements.

Skills

C++

Rust

Profiling

Performance debugging

Concurrency

Memory ownership

Large codebase

Browser engine knowledge

Tools

Gecko

Servo

Blink

WebKit

Job description

• 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
• 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

Benefits

• Health and wellness: Mozilla covers medical, dental and vision plan premiums at 100% for U.S. and Canadian employees. Our offerings give you the options you need to manage your health — and your family’s — the way you want.
• Mental health: Mental health is as important as our physical health. That’s why Mozilla’s health benefits include therapy and coaching sessions to make sure our people have access to the care they need.
• Time away: With all of life’s demands, time away from work to disconnect and recharge is essential. In addition to country-specific holidays (12 in the U.S. and Canada), vacation and sick time start accruing right away (specifics vary by country). Everyone also takes a pause together on quarterly all-company wellness days, plus you get to celebrate the most personal holiday of all: your birthday.
• Parental leave: While Mozilla’s parental leave policies vary globally, our U.S. and Canadian-based employees can look forward to 26 weeks of paid leave for childbearing parents and 12 weeks of paid leave for non-childbearing parents.
• Financial: Mozilla is a private company, so our compensation isn’t tied to stock options or equity plans. Instead, we offer generous, performance-based bonus plans to all regular employees to underscore that we share in our success as one team. As for retirement savings for US and Canadian employees, Mozilla contributes a percentage of your eligible base salary each year to the 401(k) Plan/RRSP (regardless of whether you contribute or not), with 100% vesting.
• Learning and development: We’re big believers in learning by doing, and we also want to invest in your education and development beyond your role. Every employee is eligible for an annual professional development budget. Mozillians can put it toward technical or management training, certifications, conferences and more.
• Help when you need it: Life is full of surprises; that’s why it’s important to be prepared. Mozilla provides Life/AD&D and Short and Long Term Disability insurance (offerings may vary by locale) to ensure that you and your family will have a safety net in place should you ever need it.
• Plus a bit more: A few other benefits include a quarterly wellbeing stipend (to use on those things just for you), an employee referral bonus, internet reimbursement if you’re remote, and a budget for office essentials to make working remotely ergonomically comfortable.

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 directionExperience 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 failsDeep 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 subsystemsCuriosity 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 nextA 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 systemA 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 behaviorStrong 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 workContributions to Gecko, Servo, Blink, WebKit, or another browser engineExperience maintaining an open‑source projectTechnical leadership in a small team building a new productExperience with accessibility infrastructure, browser security, profiling, or automated evaluation of agent workflows

• 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