Examine source code of UnitSwift

{
  "manifest_version": 2,
  "name": "UnitSwift",
  "version": "1.0",
  "description": "Convert units instantly! Enter a value in a sleek pop-up to switch between length, weight, or temperature units",
  "permissions": [],
  "browser_action": {
    "default_popup": "unit_convert.html",
    "default_icon": "swift_icon.png"
  },
  "icons": {
    "48": "swift_icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{2c318ba0-b057-4b5f-a931-2b8bd598953e}"
    }
  }
}