Examine source code of GifsOnTumblr

{
  "name": "GifsOnTumblr",
  "version": "1.1.2",
  "manifest_version": 2,
  "description": "Brings GIFs back to Tumblr blogs/dashboard instead of WEBPs",
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "permissions": [
    "<all_urls>"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{0eab3b64-d273-4468-9031-f0d56e2a3afc}"
    }
  }
}