Markdown Viewer

Fast, safe, in-place rendering of markdown files (.md, .mdx, .markdown, .txt) — local (file://) and remote — for Chrome and Firefox.

GFM (tables, task lists, footnotes, strikethrough, autolinks), syntax-highlighted code, KaTeX math, Mermaid diagrams, emoji shortcodes, TOC sidebar with scrollspy, GitHub light/dark themes, raw view toggle, and auto-reload for local files. All rendering is sanitized with DOMPurify before touching the DOM.

Develop

Uses pnpm (npm i -g pnpm if you don't have it).

pnpm install
pnpm dev             # Chrome with HMR
pnpm dev:firefox     # Firefox
pnpm test            # unit tests (vitest)
pnpm build           # both browsers → output/
pnpm e2e             # Playwright (requires pnpm build first)
pnpm lint:firefox    # AMO linter over the Firefox build
pnpm zip             # store-ready packages

Install

Step-by-step guides with screenshots-level detail:

• Chrome install guide
• Firefox install guide

Quick version: build with pnpm install && pnpm build, then load output/chrome-mv3 unpacked in Chrome (and enable Allow access to file URLs), or output/firefox-mv3/manifest.json as a temporary add-on in Firefox (and grant site access under Manage Extension → Permissions).

Store notes

• Permissions: storage (settings sync), declarativeNetRequest (strips restrictive CSP headers only on main-frame .md navigations that actually return raw markdown — scoped by response content-type on Chrome, github.com-excluded on Firefox), host access limited to *.md/*.markdown/*.mkd/*.txt URL patterns.
• Never renders HTML pages (content-type + raw-text detection), never runs on github.com, and any site can be disabled via the popup's "Disabled sites" list.
• No remote code; every library is bundled. Mermaid loads lazily from the bundle only when a document contains a diagram.
• Known limitation: Firefox's per-file origin policy can block auto-reload polling of file:// documents; rendering itself is unaffected.

License

MIT