Examine source code of YouFull

{
  "manifest_version": 2,
  "name": "YouFull",
  "version": "1.2resigned1",
  "description": "Plays youtube video in fullscreen",
  "icons": {
    "48": "icons/youfull-48.png"
  },
  "permissions": [
    "tabs"
  ],
  "browser_action": {
    "default_icon": "icons/youfull-48.png",
    "default_title": "Play Fullscreen"
  },
  "page_action": {
    "show_matches": [
      "https://*.youtube.com/*"
    ],
    "browser_style": true,
    "default_icon": {
      "48": "icons/youfull-48.png"
    },
    "default_title": "Play Fullscreen"
  },
  "background": {
    "scripts": [
      "youfull.js"
    ]
  },
  "applications": {
    "gecko": {
      "id": "youfull@rashy-team.com"
    }
  }
}