Examine source code of Webfonting it!

{
  "manifest_version": 3,
  "name": "Fontstorage",
  "description": "__MSG_extensionDescription__",
  "version": "3.0.3",
  "action": {
    "default_icon": "img/icon128.png",
    "default_title": "Webfonting it"
  },
  "permissions": [
    "scripting",
    "activeTab"
  ],
  "icons": {
    "16": "img/icon16.png",
    "32": "img/icon32.png",
    "48": "img/icon48.png",
    "96": "img/icon96.png",
    "128": "img/icon128.png"
  },
  "web_accessible_resources": [
    {
      "matches": [
        "<all_urls>"
      ],
      "resources": [
        "img/*.svg"
      ]
    }
  ],
  "background": {
    "scripts": [
      "js/background.js"
    ]
  },
  "homepage_url": "https://fontstorage.com/extension/",
  "default_locale": "en",
  "browser_specific_settings": {
    "gecko": {
      "id": "pull@fontstorage.com"
    }
  }
}