Examine source code of Grayscale Toggle

{
  "manifest_version": 2,
  "name": "Grayscale Toggle",
  "version": "1.0",
  "description": "Toggle grayscale mode for websites with per-site preferences",
  "browser_specific_settings": {
    "gecko": {
      "id": "grayscale-toggle@bwangc",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "permissions": [
    "activeTab",
    "storage",
    "tabs",
    "menus",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ],
  "browser_action": {
    "default_icon": "icons/icon.svg",
    "default_title": "Grayscale Toggle",
    "default_popup": "popup/popup.html"
  },
  "options_ui": {
    "page": "options/options.html",
    "open_in_tab": true
  },
  "icons": {
    "48": "icons/icon.svg",
    "96": "icons/icon.svg"
  }
}