Examine source code of URL Caster

{
  "manifest_version": 2,
  "name": "URL Caster",
  "version": "1.4.1",
  "description": "Allows the user to make quick notes by clicking a button and entering text into the resulting popup. The notes are saved in storage. See https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Examples#quicknote",
  "icons": {
    "64": "icons/link.png"
  },
  "permissions": [
    "storage",
    "tabs",
    "activeTab",
    "*://cosmicpictures.co.uk/port/urlCaster.php/*"
  ],
  "browser_action": {
    "default_icon": {
      "64": "icons/link.png"
    },
    "default_title": "URL Caster",
    "default_popup": "panel.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  }
}