Examine source code of ToMarkdown

{
  "manifest_version": 2,
  "name": "ToMarkdown",
  "version": "1.2",
  "description": "Try to generate a markdown version of current webpage.",
  "icons": {
    "48": "icons/icon.png"
  },
  "browser_action": {
    "default_icon": "icons/icon.png",
    "default_title": "Convert to Markdown",
    "default_popup": "popup/popup.html"
  },
  "permissions": [
    "activeTab",
    "storage",
    "<all_urls>"
  ],
  "options_page": "options.html",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{bb72c2ee-6bec-4752-ae59-c10fa7f62af1}"
    }
  }
}