Examine source code of TimestampHelper

{
  "name": "TimestampHelper",
  "version": "1.0.1",
  "description": "Display human-readable timestamps from selected unix timestamps",
  "author": "Haylee Schäfer (inventivetalent)",
  "icons": {
    "32": "img/clock-stamp-x32.png",
    "64": "img/clock-stamp-x64.png",
    "128": "img/clock-stamp-x128.png",
    "256": "img/clock-stamp-x256.png",
    "512": "img/clock-stamp-x512.png"
  },
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "manifest_version": 2
}