Examine source code of Custom Font Changer

{
  "manifest_version": 2,
  "name": "Custom Font Changer",
  "version": "1.0",
  "description": "Change the font family of all opened tabs and websites.",
  "permissions": [
    "activeTab",
    "<all_urls>",
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icons/icon-48.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    }
  ],
  "icons": {
    "48": "icons/icon-48.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{836007b5-f5db-4fc5-a4c1-cd6b72dd467c}"
    }
  }
}