Examine source code of Theme Changer Pro

{
  "manifest_version": 2,
  "name": "Theme Changer Pro",
  "version": "1.0",
  "description": "Automatically changes Firefox theme based on time of day.",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "theme"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icons/icon-48.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{64d998a1-d76b-481f-9bf8-58773269a116}"
    }
  }
}