Examine source code of Silent FB

{
  "name": "__MSG_extName__",
  "description": "__MSG_extIntro__",
  "default_locale": "en",
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "version": "2.0.0",
  "browser_action": {
    "default_title": "Make Facebook grayscale to avoid overstimulation"
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.facebook.com/*"
      ],
      "css": [
        "content.css"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "manifest_version": 2
}