Examine source code of GrayMode

{
  "manifest_version": 2,
  "name": "GrayMode",
  "description": "Focus better by turning distracting sites grayscale",
  "version": "1.0.0",
  "icons": {
    "16": "icons/icon-16.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "permissions": [
    "storage",
    "activeTab",
    "tabs",
    "<all_urls>"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "graymode@exts.dev",
      "strict_min_version": "142.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_start",
      "js": [
        "content-scripts/content.js"
      ]
    }
  ]
}