Examine source code of Contrast Checker Overlay

{
  "manifest_version": 2,
  "name": "Contrast Checker Overlay",
  "version": "1.0.0",
  "description": "Show heatmap overlay of text/background contrast on the page (green=good, red=bad).",
  "default_locale": "en",
  "permissions": [
    "activeTab",
    "storage"
  ],
  "browser_action": {
    "default_title": "Contrast Checker",
    "default_popup": "popup.html",
    "default_icon": "icons/icon-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_script.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "contrastchecker@example.com",
      "strict_min_version": "58.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": []
      }
    }
  }
}