Examine source code of SaveAsPNG

{
  "manifest_version": 2,
  "name": "SaveAsPNG",
  "version": "1.0",
  "description": "Allows you to download any image as png",
  "icons": {
    "64": "icons/64.png"
  },
  "permissions": [
    "menus",
    "activeTab"
  ],
  "background": {
    "scripts": [
      "scripts/main.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{009ab0a9-a329-42de-aee5-58929f250ef2}"
    }
  }
}