Examine source code of View in Steam

{
  "manifest_version": 2,
  "name": "View in Steam",
  "version": "1.1resigned1",
  "description": "Adds a button on Steam store pages to open inside of the Steam client.",
  "icons": {
    "48": "icon-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://store.steampowered.com/app/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{440b8af2-e416-40db-9457-13c4d61a8b23}"
    }
  }
}