Examine source code of Facebook To Gray

{
  "manifest_version": 2,
  "name": "Facebook To Gray",
  "version": "1.1",
  "description": "Fades your facebook feed to black & white while you scroll",
  "icons": {
    "48": "icons/fb-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.facebook.com/*"
      ],
      "js": [
        "facebooktogray.js"
      ]
    }
  ]
}