Examine source code of WallhavenDL

{
  "manifest_version": 2,
  "name": "WallhavenDL",
  "version": "1.0.1",
  "description": "Adds a download button for Wallhaven wallpapers.",
  "icons": {
    "48": "icons/download-48.png"
  },
  "permissions": [
    "downloads"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://wallhaven.cc/w/*"
      ],
      "js": [
        "whdl-cs.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "whdl-bg.js"
    ]
  }
}