Examine source code of Select to Call

{
  "name": "Select to Call",
  "version": "0.0.2",
  "manifest_version": 2,
  "description": "Select the phone number and call it.",
  "icons": {
    "16": "images/icon-on-16.png",
    "32": "images/icon-on-32.png",
    "48": "images/icon-on-48.png",
    "128": "images/icon-on-128.png"
  },
  "permissions": [
    "tabs",
    "activeTab",
    "storage",
    "http://*/",
    "https://*/"
  ],
  "web_accessible_resources": [
    "images/*",
    "select-to-call.css"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_action": {
    "default_icon": {
      "16": "images/icon-off-16.png",
      "32": "images/icon-off-32.png",
      "48": "images/icon-off-48.png",
      "128": "images/icon-on-128.png"
    }
  }
}