Examine source code of Click to Call

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "name": "Click to Call",
  "version": "2.0.0",
  "manifest_version": 2,
  "description": "Enables 'Click to Call' by converting phone numbers into clickable links.",
  "browser_specific_settings": {
    "gecko": {
      "id": "clicktocall@nickiacullo.com"
    }
  },
  "permissions": [
    "storage",
    "contextMenus",
    "tabs"
  ],
  "background": {
    "persistent": false,
    "scripts": [
      "common.js",
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*",
        "file:///*/*"
      ],
      "js": [
        "common.js",
        "content_script.js"
      ],
      "run_at": "document_idle",
      "all_frames": true
    }
  ],
  "browser_action": {
    "default_title": "Click to Call - Page Options",
    "default_popup": "browser_action.html",
    "theme_icons": [
      {
        "light": "icons/icon-16-light.png",
        "dark": "icons/icon-16.png",
        "size": 16
      },
      {
        "light": "icons/icon-32-light.png",
        "dark": "icons/icon-32-light.png",
        "size": 32
      },
      {
        "light": "icons/icon-64-light.png",
        "dark": "icons/icon-64-light.png",
        "size": 64
      }
    ]
  },
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "64": "icons/icon-64.png",
    "96": "icons/icon-96.png",
    "128": "icons/icon-128.png"
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": false,
    "browser_style": true,
    "chrome_style": true
  }
}