Examine source code of Grayscale Web

{
  "manifest_version": 2,
  "name": "Grayscale Web",
  "version": "1.0",
  "description": "Apply a grayscale filter to webpages to reduce distractions.",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icons/grayscale-48.png",
    "default_popup": "popup.html",
    "default_title": "Toggle Grayscale"
  },
  "icons": {
    "48": "icons/grayscale-48.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{b44619e1-dbd8-4d1d-8eff-1942d292cdc8}"
    }
  }
}