Examine source code of Screeny

{
  "manifest_version": 2,
  "name": "Screeny",
  "description": "A browser extension made by Belven to screenshot your browser tab easily.",
  "version": "1.0",
  "icons": {
    "16": "icon16x16.png",
    "32": "icon32x32.png",
    "48": "icon48x48.png",
    "128": "icon128x128.png"
  },
  "browser_action": {
    "default_icon": "icon16x16.png",
    "default_popup": "popup.html",
    "default_title": "Screenshot this page."
  },
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{80a32002-4db1-4c05-82ef-f3ad190864f4}"
    }
  }
}