Daniel Holbert
Software Engineer at Mozilla Corporation
California, United States
Summary
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RockstarDaniel Holbert is a seasoned software engineer with 18 years of experience focused on browser internals, layout, CSS, and SVG, currently contributing as a platform engineer at Mozilla working on Firefox. He blends deep front-end rendering expertise with systems-level contributions, from CSS serialization and containment features in Servo to canvas and input fixes in Gecko. Daniel is an active open-source maintainer and tester, improving Web Platform Tests and editing W3C CSS drafts to keep specs and implementations aligned. His work spans practical bug fixes, build reliability improvements in record-and-replay tooling, and careful documentation edits that improve clarity for other implementers. Based in California, he combines meticulous code hygiene—adding overrides and fixing compiler warnings—with a knack for subtle UX and rendering edge cases. Colleagues rely on him to bridge specification, testing, and engine code in ways that make browser rendering more predictable and interoperable.
18 years of coding experience
Github Skills (39)
debugging10
debug10
javascript10
c-language10
servo10
canvas10
testing10
css10
user-interface10
typos10
flexbox10
front-end-development10
web-standards10
html10
rust10
Programming languages (23)
Github contributions (5)
mozilla/gecko-dev
Mar 2011 - Jan 2023
Read-only Git mirror of the Mercurial gecko repositories at https://hg.mozilla.org. How to contribute: https://firefox-source-docs.mozilla.org/contributing/contribution_quickref.html
Role in this project:
Front-end Developer
Front-end DeveloperContributions:1241 commits in 11 years 11 months
Contributions summary:Daniel contributed to the Firefox rendering engine, specifically focusing on improvements to the HTML input element and canvas rendering. They addressed bugs related to mousewheel behavior in number and range input fields, adding a preference to control the feature. Furthermore, the user added rendering tests for the `mozPrintCallback` functionality in the canvas element, which involves printing with scaling and different text/rect configurations.
repositoriesfirefoxmercurialgit-mirrormozilla
web-platform-tests/wpt
Aug 2018 - Jan 2023
Test suites for Web platform specs — including WHATWG, W3C, and others
Role in this project:Test Automation Engineer
Test Automation EngineerContributions:52 reviews, 65 commits, 29 PRs in 4 years 5 months
Contributions summary:Daniel primarily contributed to the repository by modifying and adding Web Platform Tests (WPTs). Their commits focused on ensuring that the test suites for web platform specs are accurate and comprehensive. This included fixing test failures, adjusting test expectations to align with observed browser behavior, and adding new tests to cover specific features. They primarily interact with HTML, CSS and JavaScript, as well as SVG tests, and the testing frameworks and their tooling.
microsoft-edgetest-runnerspecssafarifirefox
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