_blank

manifest.json

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "manifest_version": 2,
  "name": "_blank",
  "description": "Put a double purple border around links that will open in a new tab (i.e. have target=\"_blank\")",
  "version": "1.2.1",
  "icons": {
    "128": "icon128.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_icon": "icon.png"
  },
  "permissions": [
    "https://*/*",
    "http://*/*",
    "tabs"
  ]
}