Examine source code of CallSwitch

{
  "author": "TelcoSwitch Limited",
  "background": {
    "scripts": [
      "call_action.js"
    ]
  },
  "content_scripts": [
    {
      "all_frames": true,
      "js": [
        "google_phone_lib.js"
      ],
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_start"
    },
    {
      "all_frames": false,
      "js": [
        "highlight_numbers.js"
      ],
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_end"
    }
  ],
  "description": "Use CallSwitch to call numbers in Firefox.",
  "icons": {
    "16": "app16.png",
    "32": "app32.png",
    "48": "app48.png",
    "64": "app64.png",
    "128": "app128.png"
  },
  "manifest_version": 2,
  "name": "CallSwitch",
  "permissions": [
    "tabs",
    "webNavigation",
    "contextMenus",
    "webRequest",
    "storage",
    "<all_urls>"
  ],
  "version": "5.0.1.5",
  "web_accessible_resources": [
    "icon.jpg",
    "detectAjax.js"
  ]
}