Examine source code of Custom Input Macros

{
  "manifest_version": 2,
  "name": "Custom Input Macros",
  "version": "1.0",
  "description": "Automatically replace shortcuts like /addr with full text in input fields.",
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{9b7dd1b0-d05f-4f1e-8cce-610b4454de97}"
    }
  }
}