Examine source code of Tetris+

{
  "manifest_version": 2,
  "name": "Tetris+",
  "description": "Tetris but better",
  "version": "1.0",
  "icons": {
    "48": "icons/icon.png"
  },
  "browser_action": {
    "default_icon": "icons/icon.png",
    "default_popup": "popup.html",
    "default_title": "Tetris+"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{4bf8dc3c-1cdc-47ff-8a07-f0dc9ed0c4ae}"
    }
  }
}