Examine source code of Github Durations

{
  "manifest_version" : 3 ,
  "name" : "Github Durations",
  "version" : "1.0",
  "description" : "A browser extension that shows duration between events in the timeline on GitHub.",
  "permissions" : [
    "tabs" ,
    "activeTab" ,
    "scripting" 
  ],
  "background" : {
    "scripts" : [
      "background.js" 
    ]
  },
  "action" : {
    "default_icon" : {
      "16" : "images/icon-16.png",
      "48" : "images/icon-48.png",
      "128" : "images/icon-128.png"
    }
  },
  "icons" : {
    "16" : "images/icon.png",
    "48" : "images/icon.png",
    "128" : "images/icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "hammad.fauz_githubDurations@gmail.com",
      "strict_min_version": "91.0"
    }
  }
}