Examine source code of IPVN Click To Dial

{
  "manifest_version": 2,
  "name": "IPVN Click To Dial",
  "description": "Ability to dial numbers on webpage to VoIP user.",
  "version": "0.1",
  "icons": {
    "16": "assets/icon16x16.png",
    "32": "assets/icon32x32.png",
    "48": "assets/icon48x48.png",
    "128": "assets/icon128x128.png",
    "150": "assets/icon150x150.png"
  },
  "browser_action": {
    "default_title": "IPVN Click To Dial",
    "default_popup": "src/click-to-dial.html"
  },
  "background": {
    "scripts": [
      "src/js/lib/jquery.min.js",
      "src/js/background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "src/js/number-buttons.js"
      ],
      "run_at": "document_end"
    }
  ],
  "permissions": [
    "contextMenus",
    "tabs"
  ]
}