Examine source code of Grayscale Focus Mode

{
  "manifest_version": 2,
  "name": "Grayscale Focus Mode",
  "version": "1.0",
  "description": "Turns all images grayscale except when hovered, to reduce distraction.",
  "permissions": [
    "activeTab"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Grayscale Focus Mode",
    "default_icon": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{530102cc-4f64-4d89-a7ba-7333b79cd7fd}"
    }
  }
}