Examine source code of The Browser Lock

{
  "manifest_version": 2,
  "name": "The Browser Lock",
  "version": "1.1",
  "description": "It asks the user to confirm when they want to leave the page. And that the information entered by the user may not be saved. Helpful when the page dose not support autosave.",
  "icons": {
    "48": "icons/ico.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.google.com/forms/*",
        "*://*.smartsheet.com/*",
        "*://*.microsoft.com/*",
        "*://*.office.com/*"
      ],
      "js": [
        "action.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{3dac74cd-bd42-4d8b-bb47-b1a4269642f0}"
    }
  }
}