Examine source code of Hover Beats

{
  "manifest_version": 2,
  "name": "Hover Beats (Hover-driven tiny notes)",
  "version": "1.0",
  "description": "Play a tiny musical note when you hover images, links, buttons and other elements.",
  "icons": {},
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "hover-beats.js"
      ],
      "run_at": "document_end"
    }
  ],
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{91833bbc-e9c7-40d4-a0d7-f6f7268d2055}"
    }
  }
}