Examine source code of streamable-dl

{
  "manifest_version": 2,
  "name": "streamable-dl",
  "version": "1.0",
  "description": "Adds a download link for streamable videos.",
  "icons": {
    "48": "icons/dl-48.png",
    "96": "icons/dl-96.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://streamable.com/*"
      ],
      "js": [
        "streamable-dl.js"
      ]
    }
  ]
}