Examine source code of Contextual

{
  "manifest_version": 2,
  "name": "Contextual",
  "version": "1.0.1",
  "description": "Search selected text in custom search engines.",
  "icons": {
    "48": "assets/icons/logo.svg"
  },
  "permissions": [
    "contextMenus",
    "storage",
    "activeTab"
  ],
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "contextual@londonchaim.com",
      "strict_min_version": "58.0"
    }
  }
}