Examine source code of Tab Critter

{
  "manifest_version": 2,
  "name": "Tab Critter",
  "description": "Tab Critter loves to eat your tabs. But only the old ones you just forgot to close.",
  "version": "1.0.4resigned1",
  "icons": {
    "16": "icon.png",
    "48": "icon.png",
    "128": "icon.png"
  },
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "tabs",
    "storage"
  ],
  "homepage_url": "http://www.cilb.de",
  "applications": {
    "gecko": {
      "id": "tab-critter@cilb.de",
      "strict_min_version": "57.0"
    }
  }
}