Examine source code of Header Editor FG

{
  "manifest_version" : 2 ,
  "name" : "Header Editor",
  "version" : "1.3",
  "description" : "A Mozilla extension to add, modify, and remove HTTP headers.",
  "permissions" : [
    "webRequest" ,
    "webRequestBlocking" ,
    "<all_urls>" ,
    "storage" 
  ],
  "background" : {
    "scripts" : [
      "background.js" 
    ],
    "persistent" : true 
  },
  "browser_action" : {
    "default_popup" : "popup.html",
    "default_title" : "Header Editor"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{ee543fec-4af0-44e7-9d1b-e826a5a67d61}"
    }
  }
}