Examine source code of TwitLongerExt

{
  "manifest_version": 2,
  "name": "TwitLongerExt",
  "version": "0.1.1",
  "description": "A browser extension that will automatically give a redirect to TwitLonger when a tweet is filled.",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "storage",
    "tabs"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.twitter.com/*"
      ],
      "js": [
        "TwitLongerExtRead.js"
      ]
    },
    {
      "matches": [
        "*://*.twitlonger.com/post"
      ],
      "js": [
        "TwitLongerExtDeploy.js"
      ]
    }
  ]
}