Examine source code of New Tab Indicator

{
  "manifest_version": 2,
  "version": "0.2",
  "browser_specific_settings": {
    "gecko": {
      "id": "new-tab-indicator@chrischen.me"
    }
  },
  "name": "New Tab Indicator",
  "description": "Adds an icon next to the mouse cursor when hovering over a link that will open in a new tab or window.",
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "new-tab-indicator.js"
      ]
    }
  ]
}