Examine source code of SteamURLOpenInSteam

{
  "manifest_version": 2,
  "name": "SteamURLOpenInSteam",
  "version": "1.0",
  "description": "Opens steamURLs in the steam app",
  "icons": {
    "48": "Steam.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.steampowered.com/*",
        "*://steamcommunity.com/*"
      ],
      "js": [
        "SteamURL.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{712bf039-9af0-49f6-9eed-8d1a7e252680}"
    }
  }
}