Examine source code of Fast theme toggle

{
  "manifest_version": 2,
  "name": "Fast theme toggle",
  "description": "Fast theme toggle enable to quickly switch the website theme.",
  "version": "1.0.13",
  "background": {
    "scripts": [
      "src/scripts/background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://*/*",
        "http://*/*",
        "file:///*/*"
      ],
      "run_at": "document_start",
      "css": [
        "src/styles/theme.css"
      ],
      "js": [
        "src/scripts/helper.js",
        "src/scripts/content.js"
      ]
    },
    {
      "matches": [
        "https://*/*",
        "http://*/*",
        "file:///*/*"
      ],
      "run_at": "document_idle",
      "js": [
        "src/scripts/helper.js"
      ]
    }
  ],
  "web_accessible_resources": [
    "src/scripts/helper.js"
  ],
  "browser_action": {
    "default_title": "Fast theme toggle"
  },
  "icons": {
    "16": "src/images/icon16.png",
    "48": "src/images/icon48.png",
    "128": "src/images/icon128.png"
  },
  "incognito": "spanning",
  "browser_specific_settings": {
    "gecko": {
      "id": "{fc356679-6d82-4915-8511-957d1db936ac}"
    }
  }
}