Examine source code of GMX Mail Checker

{
  "manifest_version": 2,
  "version": "0.1.1",
  "name": "GMX Mail Checker",
  "description": "Check gmx.com for unread emails and get badge area counter without the need to enter your credentials (password)",
  "permissions": [
    "*://*.gmx.com/*",
    "history",
    "alarms",
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "16": "data/icons/16.png",
    "19": "data/icons/19.png",
    "32": "data/icons/32.png",
    "38": "data/icons/38.png",
    "48": "data/icons/48.png",
    "64": "data/icons/64.png",
    "128": "data/icons/128.png",
    "256": "data/icons/256.png",
    "512": "data/icons/512.png"
  },
  "browser_action": {
    "default_icon": {
      "16": "data/icons/16.png",
      "19": "data/icons/19.png",
      "32": "data/icons/32.png",
      "38": "data/icons/38.png",
      "48": "data/icons/48.png",
      "64": "data/icons/64.png"
    }
  },
  "homepage_url": "https://add0n.com/gmx-mail-checker.html",
  "content_scripts": [
    {
      "matches": [
        "https://navigator-bs.gmx.com/*"
      ],
      "js": [
        "data/inject.js"
      ]
    }
  ]
}