Examine source code of FontExplorer

{
  "manifest_version" : 3 ,
  "name" : "FontExplorer",
  "version" : "1.0",
  "description" : "Web Font Analyzer and Tester by TypeVista",
  "browser_specific_settings": {
    "gecko": {
      "id": "fontexplorer@typevista.tools"
    }
  },
  "icons" : {
    "48" : "icons/icon-48.png",
    "96" : "icons/icon-96.png"
  },
  "permissions" : [
    "activeTab" ,
    "storage" 
  ],
  "background" : {
    "scripts" : [
      "background.js" 
    ]
  },
  "action" : {
    "default_popup" : "popup/popup.html",
    "default_icon" : {
      "48" : "icons/icon-48.png",
      "96" : "icons/icon-96.png"
    }
  },
  "content_scripts" : [
    {
      "matches" : [
        "<all_urls>" 
      ],
      "js" : [
        "content_scripts/fontAnalyzer.js" 
      ]
    }
  ],
  "options_ui" : {
    "page": "options/options.html" ,
    "open_in_tab": true
  }
}