Examine source code of Dev Mode

{
  "manifest_version" : 2 ,
  "name" : "Dev Mode",
  "version" : "1.0.1",
  "description" : "A simple helper extension for developers working on localhost environments.",
  "browser_specific_settings": {
    "gecko": {
      "id": "devmode@d7om.dev"
    }
  },
  "permissions" : [
    "activeTab" ,
    "storage" 
  ],
  "content_scripts" : [
    {
      "matches" : [
        "*://localhost/*" ,
        "*://127.0.0.1/*" 
      ],
      "js" : [
        "content.js" ,
        "utils.js" 
      ],
      "css" : [
        "styles.css" 
      ],
      "run_at" : "document_end" 
    }
  ],
  "icons" : {
    "48" : "icon48.png",
    "96" : "icon96.png",
    "128" : "icon128.png"
  },
  "homepage_url" : "https://github.com/d7omdev/devmode"
}