Examine source code of NFL nofollowLink

{
  "manifest_version": 2,
  "name": "NFL nofollowLink",
  "version": "1.2resigned1",
  "description": "Highlights links and color them differently according to nofollow or not status. The icons in the search bar allow you to enable or disable the extension",
  "icons": {
    "48": "icons/NFLlogo.png"
  },
  "background": {
    "scripts": [
      "nfl.js"
    ]
  },
  "page_action": {
    "default_icon": "icons/off.svg",
    "browser_style": true
  },
  "permissions": [
    "activeTab",
    "tabs"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{947de141-a859-46c2-881f-f359dc778208}"
    }
  }
}