Add Chrome extension for rendering markdown files

[Copilot]

Implements a Chrome browser plugin that automatically renders .md files (local and remote) with GitHub-flavored markdown styling.

Implementation

• manifest.json: Manifest V3 extension config with content script injection on all URLs
• content.js: Detects .md files by URL extension, extracts raw content, parses with marked.js, replaces DOM with styled HTML
• markdown.css: GitHub-inspired responsive styling (headers, code blocks, tables, lists, blockquotes, task lists)
• marked.min.js: GFM-compatible markdown parser (41KB)
• Icons: 16/48/128px PNG assets

Usage

After loading the unpacked extension:

• Navigate to any .md URL (remote: https://example.com/README.md, local: file:///path/to/file.md)
• Extension auto-detects and renders with formatting

// Core detection and rendering logic
if (pathname.toLowerCase().endsWith('.md')) {
  const markdown = document.body.textContent;
  const html = marked.parse(markdown);
  document.body.innerHTML = `<div class="markdown-body">${html}</div>`;
}

Screenshots

Before (raw text):

After (rendered):

Notes

• Runs entirely client-side, no external API calls
• Local file access requires enabling "Allow access to file URLs" in extension settings
• Supports all standard markdown features (nested lists, code blocks, tables, task lists, etc.)

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• cdn.jsdelivr.net
  • Triggering command: /usr/bin/curl curl -o marked.min.js REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

Implement a chrome browser plugin to render any local or remote markdown file ending with a .md file extension

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