Examine source code of Monochrome Mode

{
  "manifest_version": 2,
  "name": "Monochrome Mode",
  "version": "1.0",
  "description": "Temporarily convert all images on the page to black and white to reduce distractions.",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{dbb1dd5c-bbd0-4dcd-9dc5-62823d316823}"
    }
  }
}