Examine source code of Obscuritas

{
  "manifest_version": 2,
  "name": "Obscuritas",
  "version": "3.0",
  "description": "Firefox dark mode extension that replace all light colors to dark colors on every page by JS.",
  "icons": {
    "48": "icons/obscuritas-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_start",
      "js": [
        "obscuritas.js"
      ]
    }
  ],
  "web_accessible_resources": [
    "script.js"
  ]
}