Examine source code of Dev Toolbox

{
  "name": "Dev Toolbox",
  "description": "Dev Toolbox provides quick offline access to various development tools.",
  "version": "1.1.8",
  "manifest_version": 2,
  "permissions": [
    "storage"
  ],
  "browser_action": {
    "default_popup": "index.html",
    "default_icon": {
      "16": "/img/tb_16.png",
      "24": "/img/tb_24.png"
    }
  },
  "icons": {
    "16": "/img/tb_16.png",
    "24": "/img/tb_24.png",
    "32": "/img/tb_32.png",
    "48": "/img/tb_48.png",
    "128": "/img/tb_128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{37ac6010-f513-4f04-a96f-aa22b34d386f}"
    }
  }
}