Examine source code of Media previewer

{
  "manifest_version": 2,
  "name": "Media previewer",
  "author": "Pythack",
  "version": "1.0.3",
  "description": "Preview media by hovering over its URL",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "previewer.js"
      ],
      "css": [
        "previewer.css"
      ]
    }
  ],
  "permissions": [
    "<all_urls>",
    "storage"
  ],
  "browser_action": {
    "default_icon": "iconactive.png",
    "default_title": "Media previewer",
    "browser_style": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{f379a0ce-0087-4fee-a90c-2bd3de67cbac}"
    }
  }
}