Examine source code of Site Tracker

{
  "manifest_version": 2,
  "name": "Site Tracker",
  "version": "1.0",
  "description": "Enables you to save a website under a certain category.",
  "icons": {
    "225": "st.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.mozilla.org/*"
      ],
      "js": [
        "index.js",
        "tab.js"
      ]
    }
  ],
  "browser_action": {
    "default_icon": "st.png",
    "default_title": "Site Tracker",
    "default_popup": "index.html"
  },
  "permissions": [
    "tabs"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{5f14f68c-cb3d-42e9-a105-15444faf2bf7}"
    }
  }
}