Examine source code of Twitter-feed Block

{
  "manifest_version": 2,
  "name": "Twitter-feed Block",
  "version": "1.0",
  "description": "Blocks all of twitter except direct links to posts.",
  "icons": {
    "48": "twitter.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://twitter.com/*"
      ],
      "js": [
        "twitter_block.js"
      ]
    }
  ]
}