Examine source code of faceblock

{
  "manifest_version": 2,
  "name": "faceblock",
  "version": "1.1",
  "description": "Installing this extension will block all websites linked to facebook.",
  "author": "Seburo",
  "content_scripts": [
    {
      "matches": [
        "*://*.facebook.com/*",
        "*://*.snaptu.com/*",
        "*://*.gowalla.com/*",
        "*://*.instagram.com/*",
        "*://*.lightbox.com/*",
        "*://*.getspool.com/*",
        "*://*.atlassolutions.com/*",
        "*://*.parseplatform.org/*",
        "*://*.onavo.com/*",
        "*://*.whatsapp.com/*",
        "*://*.oculus.com/*",
        "*://*.privatecore.com/*",
        "*://*.tbhtime.com/*",
        "*://*.sanzaru.com/*",
        "*://*.meta.com/*",
        "*://*.giphy.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    },
    {
      "matches": [
        "*://*.facebook.com/*",
        "*://*.snaptu.com/*",
        "*://*.gowalla.com/*",
        "*://*.instagram.com/*",
        "*://*.lightbox.com/*",
        "*://*.getspool.com/*",
        "*://*.atlassolutions.com/*",
        "*://*.parseplatform.org/*",
        "*://*.onavo.com/*",
        "*://*.whatsapp.com/*",
        "*://*.oculus.com/*",
        "*://*.privatecore.com/*",
        "*://*.tbhtime.com/*",
        "*://*.sanzaru.com/*",
        "*://*.meta.com/*",
        "*://*.giphy.com/*"
      ],
      "js": [
        "aftercontent.js"
      ],
      "run_at": "document_end"
    }
  ]
}