Examine source code of Twitter Highlighter

{
  "manifest_version": 2,
  "name": "Twitter Highlighter",
  "version": "1.0",
  "description": "Highlight and share selected text on Twitter.",
  "permissions": [
    "activeTab",
    "storage",
    "contextMenus"
  ],
  "icons": {
    "48": "icon.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{6377f784-07fc-4462-91c5-f66f8020443d}"
    }
  }
}