Examine source code of multiplayer-plus-block

{
  "manifest_version": 2,
  "name": "multiplayer-plus-block",
  "description": "Blocks multiplayer.it plus pop-up",
  "version": "0.0.1",
  "icons": {
    "64": "icon.png"
  },
  "permissions": [
    "webNavigation",
    "tabs",
    "activeTab"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{6607554c-6017-4850-b3c1-6dfe5ec75d09}"
    }
  }
}