Examine source code of Shortcut Master

{
  "background": {
    "persistent": false,
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "description": "Enable additional keyboard shortcuts for closing tabs.",
  "developer": {
    "name": "k-mouse"
  },
  "icons": {
    "16": "icon_16.png",
    "19": "icon_19.png",
    "48": "icon_48.png",
    "64": "icon_64.png",
    "128": "icon_128.png"
  },
  "commands": {
    "closeAllTabs": {
      "suggested_key": {
        "default": "Alt+Shift+W"
      },
      "description": "Close all tabs"
    },
    "closeOtherTabs": {
      "suggested_key": {
        "default": "Alt+W"
      },
      "description": "Close other tabs"
    },
    "closeLeftTabs": {
      "suggested_key": {
        "default": "Alt+Q"
      },
      "description": "Close tabs to the left"
    },
    "closeRightTabs": {
      "suggested_key": {
        "default": "Alt+R"
      },
      "description": "Close tabs to the right"
    }
  },
  "manifest_version": 2,
  "name": "Shortcut Master",
  "permissions": [
    "tabs"
  ],
  "version": "1.4",
  "browser_specific_settings": {
    "gecko": {
      "id": "{59435731-d4be-4fb8-ace6-c3b945540633}"
    }
  }
}