Examine source code of MirrorPeek

{
  "manifest_version": 2,
  "name": "MirrorPeek",
  "version": "1.0",
  "description": "Toggle horizontal mirror on images in-page with optional opacity blend.",
  "permissions": [
    "<all_urls>"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_script.js"
      ],
      "run_at": "document_end"
    }
  ],
  "applications": {
    "gecko": {
      "id": "mirrorpeek@example.com"
    }
  }
}