Examine source code of night light mode

{
  "manifest_version": 2,
  "name": "night light",
  "description": "Inverted display mode for less eye strain in dark or dim lighting",
  "version": "1.15resigned1",
  "author": "dev@conceptualspace.net",
  "applications": {
    "gecko": {
      "id": "{d8a39bf7-9f46-45b7-9d77-7754cd13c0f8}"
    }
  },
  "icons": {
    "16": "icon16.png",
    "32": "icon32.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "background": {
    "scripts": [
      "underscore-min.js",
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": "icon.png",
    "default_title": "Toggle night mode"
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": false
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "content_script_start.js"
      ],
      "all_frames": true,
      "run_at": "document_start"
    },
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "content_script_idle.js"
      ],
      "all_frames": true,
      "run_at": "document_idle"
    }
  ],
  "permissions": [
    "storage",
    "contextMenus",
    "activeTab",
    "tabs",
    "http://*/*",
    "https://*/*"
  ]
}