Examine source code of MediaViewer

{
  "manifest_version": 2,
  "name": "MediaViewer",
  "version": "1.0",
  "description": "View all images and videos on a webpage in an organized gallery view.",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "applications": {
    "gecko": {
      "id": "mediaviewer@yourdomain.com"
    }
  }
}