Staff Software Engineer, Browser (New Products)

Mozilla

4d•$138,000 - $217,000•Remote

About The Position

Mozilla is seeking an experienced browser engineer to join a small team exploring new applications of browser technology. This hands-on individual contributor role combines deep systems engineering, rapid experimentation, and collaboration across technical disciplines. The engineer will own engine-level investigations and implementation while working closely with the team’s technical lead. The work involves investigating browser behavior, implementing changes deep in the engine, and evaluating which ideas produce meaningful improvements to inform technical direction. The role focuses on experiments in browser engine subsystems; efficient and accurate representation of browser state; capabilities for reliable programmatic interaction with web content; and measuring the performance and correctness of changes. It also involves profiling overhead, documenting both successful and unsuccessful experiments, and using AI tools to accelerate coding and analysis while validating their output through debugging, tests, and measurement.

Requirements

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.
Experience implementing substantial changes in a browser engine subsystem and tracing their effects into neighboring subsystems.
Strong proficiency in C++ or Rust and experience navigating a large systems codebase.
Practical knowledge of memory ownership, concurrency, object lifetimes, and performance debugging.
Ability to build JavaScript and scripting tools to exercise and measure work.
Demonstrated ability to investigate unfamiliar code, form precise hypotheses, construct useful prototypes, and interpret results.
Ability to distinguish implementation effects from variability in websites, workloads, or model behavior.
Strong understanding of web platform behavior and compatibility, including document structure, script execution, rendering, user interaction, and the challenges of accurately exposing browser internal state.
Experience with profiling, tracing, regression tests, or conformance tests, and grounding performance claims in reproducible evidence.
Ability to explain the benefits of an optimization and the circumstances in which it fails.
Curiosity about AI agents and willingness to work directly with agent harnesses and coding tools.
Ability to connect low-level implementation choices to the information an agent receives and the work it must do next.

Nice To Haves

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.

Responsibilities

Design and implement experiments within browser engine subsystems.
Investigate how internal data structures and execution behavior affect performance, correctness, and interfaces exposed to developer tools.
Evaluate approaches for representing and exposing browser state efficiently and accurately, including tradeoffs involving information loss, implementation complexity, and compatibility with dynamic web content.
Prototype engine capabilities that support reliable programmatic interaction with web content, investigating the effects of document structure, layout, navigation, and event handling.
Instrument browser behavior and evaluate changes against repeatable tasks; measure performance and correctness, isolate effects, and document successful and unsuccessful experiments.
Check that performance gains hold beyond the workloads used to develop a prototype.
Profile overhead introduced by new capabilities and pursue improvements when measurements justify them.
Use AI tools to accelerate coding and analysis, and verify their output through debugging, tests, and measurement.