Examine source code of Messenger Side Hide

{
  "manifest_version": 3,
  "name": "Messenger Side Hide",
  "version": "1.3",
  "description": "Toggle the visibility of the Side Panels on Messenger.com. https://github.com/Chikiran/Messenger-Side-Hide",
  "permissions": [
    "storage"
  ],
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icon16.png",
      "48": "icon48.png",
      "128": "icon128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.messenger.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "messengerhideside@chuuniverse"
    }
  }
}