Examine source code of gemwin88

{
  "manifest_version": 2,
  "name": "messenger photos downloader",
  "version": "1.0",
  "description": "Adds a button to messenger to download all images and videos on a messenger conversation",
  "icons": {
    "32": "icons/icon-32.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.messenger.com/t/*"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "style.css"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "downloads",
    "https://m.facebook.com/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{6a86354c-066e-4d05-a492-7982c1258cf9}"
    }
  }
}