Examine source code of Roll20 Avatar Remover

{
  "manifest_version": 2,
  "name": "Roll20 Avatar Remover",
  "version": "1.0",
  "description": "Removes the avatar container from roll20.net so you can see the map better",
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://app.roll20.net/*"
      ],
      "js": [
        "roll20-avatar-remover.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{5a1d6452-3a9c-428d-b6b2-eecba044a769}"
    }
  }
}