Examine source code of font_wizmo

{
  "manifest_version": 2,
  "name": "My Extension",
  "version": "1.0",
  "description": "A simple extension to change the font of all websites.",
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{0dad7892-ab43-44cf-8c0f-d66703ab683c}"
    }
  }
}