Examine source code of PopUpDictionary

{
  "manifest_version": 2,
  "name": "PopUpDictionary",
  "version": "1.0",
  "description": "Instant dictionary lookup with PopUpDictionary. Quickly define words and expand your vocabulary with a simple popup interface.",
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Dictionary Extension"
  },
  "icons": {
    "48": "icon.png",
    "96": "icon@2x.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{f54fafba-c2e2-40a9-885c-114499d24f52}"
    }
  }
}