Examine source code of +2 Counter

{
  "manifest_version": 2,
  "name": "+2 Counter",
  "version": "1.0",
  "description": "counts and displays +2's in a twitch chat",
  "icons": {
    "48": "icons/border-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.twitch.tv/*"
      ],
      "js": [
        "counter.js"
      ],
      "css": [
        "style.css"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{6e51643e-f22c-4b4b-b333-15083c48b853}"
    }
  }
}