Examine source code of Downvote Hider

{
  "manifest_version": 2,
  "version": "0.1",
  "name": "downvote-hider",
  "description": "Removes downvote buttons from replies on Twitter.com.",
  "icons": {
    "48": "icons/48.png",
    "96": "icons/96.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.twitter.com/*"
      ],
      "js": [
        "index.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{0e9c9268-59c1-43af-a934-0dd054dd9662}"
    }
  }
}