Examine source code of TwitterBlock

{
  "manifest_version": 2,
  "name": "TwitterBlock",
  "version": "0.2.8",
  "description": "Removes promoted tweets",
  "content_scripts": [
    {
      "matches": [
        "http://www.twitter.com/*",
        "https://twitter.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{3e41f9cf-2bba-4e21-ad62-525fe7cc4f03}"
    }
  }
}