Examine source code of Steam Forgetmenot

{
  "author": "Bigfootmech",
  "manifest_version": 2,
  "name": "Steam Forgetmenot",
  "version": "1.2resigned1",
  "homepage_url": "https://github.com/Bigfootmech/Steam-Forgetmenot",
  "description": "Retains cookies for machine ID (and tries to do session?) for Steam.",
  "icons": {
    "48": "icons/icon.svg",
    "96": "icons/icon.svg"
  },
  "permissions": [
    "*://steamcommunity.com/*",
    "*://store.steampowered.com/*",
    "*://help.steampowered.com/*",
    "cookies",
    "storage"
  ],
  "background": {
    "scripts": [
      "background_scripts/steam_cookies.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://steamcommunity.com/*",
        "*://store.steampowered.com/*",
        "*://help.steampowered.com/*"
      ],
      "js": [
        "content_scripts/action.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{734aa6dd-87b7-4bce-9c0a-7b4c47d37e15}"
    }
  }
}