Examine source code of Grayscale

{
  "manifest_version": 2,
  "name": "Grayscale",
  "version": "1.1resigned1",
  "author": "Truong Minh Triet",
  "description": "Turn all tabs into black-white color. Click the icon again to turn back to original color.",
  "permissions": [
    "http://*/",
    "https://*/",
    "tabs",
    "activeTab"
  ],
  "icons": {
    "48": "icons/grayscale-48.png"
  },
  "browser_action": {
    "default_icon": "icons/grayscale-48.png",
    "default_title": "Grayscale"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "/content.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "/background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{514f6ed9-066e-432d-bf3a-9b249d5d8c9f}"
    }
  }
}