Examine source code of Toggle Fullscreen Button

{
  "manifest_version": 2,
  "name": "Fullscreen",
  "version": "1.0",
  "description": "xOs style full screen button",
  "background": {
    "scripts": [
      "fullscreen.js"
    ]
  },
  "browser_action": {
    "default_icon": "icon.svg",
    "default_title": "Fullscreen",
    "scripts": [
      "fullscreen.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{21eb6871-196d-4251-9b30-5f3038dc10e1}"
    }
  }
}