Examine source code of Reduce Eye Strains - Grayscale Filter

{
  "manifest_version": 2,
  "name": "Grayscale Filter",
  "version": "2.1.4",
  "description": "Apply a clean grayscale look to every website you visit - no data collection, no tracking. Fully customizable intensity, open-source and privacy-friendly.",
  "developer": {
    "name": "Nubet",
    "url": "https://github.com/Nubet/Grayscale-Filter-Extension/"
  },
  "icons": {
    "48": "assets/icon48.png",
    "128": "assets/icon128.png"
  },
  "permissions": [
    "storage",
    "tabs",
    "<all_urls>",
    "contextMenus"
  ],
  "browser_action": {
    "default_icon": {
      "48": "assets/icon48.png",
      "128": "assets/icon128.png"
    },
    "default_title": "Grayscale Filter",
    "default_popup": "src/ui/popup.html"
  },
  "options_ui": {
    "page": "src/ui/options.html",
    "open_in_tab": true
  },
  "background": {
    "scripts": [
      "src/common/utils.js",
      "src/background/background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "src/common/utils.js",
        "src/content/content.js"
      ],
      "css": [
        "src/content/grayscale.css"
      ],
      "run_at": "document_start",
      "all_frames": true,
      "match_about_blank": true
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "grayscale-filter@nubet",
      "strict_min_version": "80.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": []
      }
    }
  }
}