Examine source code of WebSnap

{
  "manifest_version": 2,
  "name": "WebSnap",
  "version": "1.0",
  "description": "Screenshot the webpage with one click.",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "permissions": [
    "activeTab",
    "tabs",
    "<all_urls>"
  ],
  "browser_action": {
    "default_icon": "icons/icon-32.png",
    "default_title": "Snap it!"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "websnap.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{1e9419e2-b8fe-4665-aad7-337bf9714d33}"
    }
  }
}