Backend engineer building scalable AI - native cybersecurity infrastructure for Doppel. Developing software that detects and disrupts phishing, impersonation, fraud, and other digital threats.
About the role
- Browser engine specialist developing experimental browser capabilities at Mozilla, the open-source internet technology company. Investigating engine internals, performance, correctness, and AI-agent interaction.
Responsibilities
- Design and implement experiments within browser engine subsystems
- Investigate how internal data structures and execution behavior affect performance, correctness, and developer-tool interfaces
- Evaluate approaches for representing and exposing browser state efficiently and accurately
- Prototype engine capabilities supporting 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 effects of changes, and document unsuccessful and successful experiments
- Validate that gains hold beyond prototype-development workloads
- Profile overhead introduced by new capabilities and pursue measurement-backed improvements
- Use AI tools to accelerate coding and analysis, verifying output through debugging, tests, and measurement
- Work closely with the team’s technical lead as a hands-on individual contributor
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
- Strong proficiency in C++ or Rust
- 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
- Ability to investigate unfamiliar code, form precise hypotheses, construct useful prototypes, and interpret results
- Strong understanding of web platform behavior and compatibility
- Experience with profiling, tracing, regression tests, or conformance tests
- Curiosity about AI agents and willingness to work directly with agent harnesses and coding tools
- Contributions to Gecko, Servo, Blink, WebKit, or another browser engine are nice to have
- Experience maintaining an open-source project is nice to have
- Technical leadership in a small team building a new product is nice to have
- Experience with accessibility infrastructure, browser security, profiling, or automated evaluation of agent workflows is nice to have
Benefits
- Generous performance-based bonus plans for all eligible employees
- Rich medical, dental, and vision coverage
- Generous retirement contributions with 100% immediate vesting
- Quarterly all-company wellness days
- Country-specific holidays plus a birthday day off
- One-time home office stipend
- Annual professional development budget
- Quarterly well-being stipend
- Considerable paid parental leave
- Employee referral bonus program
- Other benefits including life/AD&D, disability, and EAP, varying by country
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