Examine source code of Font Swapper

{
  "manifest_version": 2,
  "name": "Local Font Switcher",
  "version": "1.2.7",
  "description": "Upload and apply custom fonts per-site.",
  "permissions": [
    "storage",
    "tabs",
    "activeTab"
  ],
  "browser_action": {
    "default_title": "Local Font Switcher",
    "default_popup": "popup.html"
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content-script.js"
      ]
    }
  ],
  "icons": {
    "48": "icon.png",
    "96": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{8b1c822a-085d-4db1-87e4-a067b42006a4}"
    }
  }
}