Protocol is Mozilla's design system for Firefox and Mozilla marketing websites, a CSS framework and markup pattern library published with source Sass files so teams can include only the styles and components a given page actually needs.
The Sass-based, pick-only-what-you-need architecture keeps CSS payload small for simple marketing pages, since it avoids shipping the full framework when a page only needs navigation and typography.
Developers building marketing or content-focused websites (not full web apps) who want a lean, configurable CSS framework rather than a full component library.
It's currently used primarily by Mozilla's own marketing team for mozilla.org, worth checking the GitHub repo directly for current install and configuration steps.
Mozilla's internal design system, focused on accessibility and responsive design.
