Examine source code of DnDBeyondBGRemover

{
  "manifest_version": 2,
  "name": "DnDBeyondBGRemover",
  "version": "1.1",
  "description": "Removes the background on dnd beyond character sheets.",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "dndbeyondbgremover@brandonost.net"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.dndbeyond.com/*"
      ],
      "js": [
        "dndbgremove.js"
      ]
    }
  ]
}