Vimium is an open-source browser extension for Chrome and Firefox that brings Vim-style keyboard navigation to the web. The codebase implements a sophisticated mode system (Normal, Insert, Find, Visual, etc.) with a central HandlerStack for event interception and bubbling. It provides link hints, a Vomnibar for URL/bookmark/tab search with autocomplete, scrolling, marks, and tab management. The architecture is split into background scripts (service worker) and content scripts injected into every page, communicating via message passing. The extension uses a custom key-mapping DSL parsed by the Commands module, and stores settings in chrome.storage. The UI (options page, help dialog, HUD, Vomnibar) is rendered in iframes with secure messaging via MessageChannel. The codebase is mature, well-tested (unit and DOM tests), and actively maintained by a community of contributors. While primarily an application, it includes a curated list of top-level domains (resources/tlds.txt) for URL parsing, but no research or data pipelines.