Examine source code of Soundman

{
  "description": "Adds context menu to control playback in tabs",
  "author": "MrOtherGuy",
  "manifest_version": 2,
  "name": "Soundman",
  "permissions": [
    "tabs",
    "<all_urls>",
    "menus",
    "storage"
  ],
  "version": "0.1.8resigned1",
  "background": {
    "scripts": [
      "background-script.js"
    ]
  },
  "options_ui": {
    "page": "options/options.html",
    "browser_style": true
  },
  "commands": {
    "smhk_playPause": {
      "suggested_key": {
        "default": "MediaPlayPause"
      },
      "description": "Toggle Play/Pause state"
    },
    "smhk_muteUnmute": {
      "suggested_key": {
        "default": "Ctrl+Shift+O"
      },
      "description": "Toggle muted state"
    }
  },
  "applications": {
    "gecko": {
      "id": "soundman@example.com",
      "strict_min_version": "61.0"
    }
  }
}