Examine source code of Theme Inverter

{
  "manifest_version": 2,
  "name": "Theme Inverter",
  "version": "1.0",
  "description": "A website theme inverter, making light & dark themes a little more comfortable to read.",
  "permissions": [
    "storage",
    "tabs",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icon16.png",
      "48": "icon48.png",
      "128": "icon128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{f419e3ab-43fe-446b-9106-54e8de1dc752}"
    }
  }
}