Examine source code of SideApp For Messenger

{
  "name": "SideApp For Messenger",
  "description": "SideApp For Messenger Allows You To Open Messenger In The Sidebar Or In A New Window.",
  "applications": {
    "gecko": {
      "id": "sbfofm.ff@Scripty_via_The.UNITY.Empire",
      "strict_min_version": "42.0"
    }
  },
  "version": "1.1.0.45",
  "permissions": [
    "storage",
    "tabs",
    "https://*.messenger.com/*",
    "http://*.messenger.com/"
  ],
  "homepage_url": "https://addons.mozilla.org/en-US/firefox/user/The_UNITY_Empire/",
  "background": {
    "page": "background.html"
  },
  "browser_action": {
    "default_icon": "messenger.png",
    "default_title": "SideApp for Messenger"
  },
  "sidebar_action": {
    "default_icon": {
      "512": "messenger.png"
    },
    "default_title": "Messenger",
    "default_panel": "index.html"
  },
  "content_scripts": [
    {
      "css": [
        "css.css"
      ],
      "js": [
        "sideapp.js",
        "cnt.js",
        "js.js"
      ],
      "matches": [
        "https://*.messenger.com/*",
        "http://*.messenger.com/"
      ]
    }
  ],
  "commands": {
    "_execute_browser_action": {
      "suggested_key": {
        "default": "Alt+M"
      },
      "description": "Messenger"
    },
    "_execute_sidebar_action": {
      "suggested_key": {
        "default": "Alt+Shift+M"
      },
      "description": "Messenger"
    }
  },
  "icons": {
    "512": "messenger.png"
  },
  "manifest_version": 2
}