Examine source code of TwitterFixer

{
  "name": "TwitterFixer",
  "version": "0.0.3resigned1",
  "manifest_version": 2,
  "description": "Puts the \"Notifications\" button back where it belongs.",
  "homepage_url": "https://tannerfilip.me",
  "icons": {
    "16": "icons/16.png",
    "48": "icons/48.png",
    "128": "icons/128.png"
  },
  "default_locale": "en",
  "permissions": [
    "tabs"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://twitter.com/"
      ],
      "css": [
        "moment-killer.css"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "@twitter-fixer"
    }
  }
}