Examine source code of Debugmode

{
  "manifest_version": 2,
  "name": "Debugmode",
  "version": "1.0.3",
  "description": "toggle debugmode on and off for when developing websites",
  "icons": {
    "48": "icons/debugmode-icon.png"
  },
  "permissions": [
    "activeTab",
    "storage"
  ],
  "browser_action": {
    "default_icon": "icons/debugmode-icon.png",
    "default_title": "Debugmode",
    "default_popup": "popup/toggle.html"
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "run_at": "document_start",
      "all_frames": true,
      "js": [
        "content_scripts/debugmode.js"
      ]
    }
  ]
}