Examine source code of Weblock

{
  "manifest_version": 2,
  "name": "Website Blocker",
  "version": "1.1",
  "description": "Block domains the easy way",
  "icons": {
    "48": "icons/blocker-48.png"
  },
  "permissions": [
    "activeTab",
    "storage",
    "<all_urls>",
    "tabs"
  ],
  "browser_action": {
    "default_icon": "icons/blocker-32.png",
    "default_title": "Website Blocker",
    "default_popup": "popup/menu.html"
  },
  "background": {
    "scripts": [
      "background/url-checker.js"
    ]
  }
}