Examine source code of ZeroWidth Detection

{
  "manifest_version": 2,
  "name": "ZeroWidth Detection",
  "version": "2.1resigned1",
  "description": "Checks websites that you visit for invisible zero-width characters and replaces them with a specified character. Has the ability to copy all the characters found.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup/popup.html",
    "default_title": "Zero-width character Detection"
  },
  "options_ui": {
    "page": "options/options.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_start",
      "js": [
        "zerowidth-detect.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "permissions": [
    "<all_urls>",
    "tabs",
    "storage",
    "webRequest",
    "clipboardRead",
    "clipboardWrite"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{70e22d9e-cd09-4c53-b5b7-27d9f049a7c2}"
    }
  }
}