Examine source code of Add to 2Do

{
  "manifest_version": 2,
  "name": "Add to 2Do",
  "version": "1.3resigned1",
  "description": "Adds a button to create a task in 2Do for the current tab.",
  "icons": {
    "18": "assets/icon-18.png",
    "36": "assets/icon-36.png",
    "64": "assets/icon-64.png"
  },
  "browser_action": {
    "default_icon": {
      "18": "assets/icon-18.png",
      "36": "assets/icon-36.png"
    },
    "default_title": "Add to 2Do"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "permissions": [
    "tabs",
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "@firefox-2do-extension"
    }
  }
}