Examine source code of Base64 Codec

{
  "name": "Base64 Codec",
  "version": "1.0.0",
  "description": "Base64 Encoder Decoder, based on contextMenu, with in-place html text replacement.",
  "manifest_version": 2,
  "background": {
    "scripts": [
      "content.js"
    ]
  },
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "128": "icons/icon128.png"
  },
  "permissions": [
    "contextMenus",
    "tabs",
    "notifications",
    "http://*/",
    "https://*/"
  ]
}