Examine source code of Pix 2 Per

{
  "manifest_version": 2,
  "name": "Pix 2 Per",
  "version": "1.1",
  "description": "Converts pixel values to percentages.",
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "pix2per.png",
      "48": "pix2per.png",
      "128": "pix2per.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "kmr22live@gmail.com"
    }
  }
}