When setting a custom icon for the app in the manifest "window":{"icon": "icon.png"}, it will show with an incorrect size under the volume mixer.
The following example shows the result of a simple app playing a YouTube video and the custom icon used in the manifest is NWJS's own icon. The icon displayed in the volume mixer is too big as you can see:

Not using a custom icon in the manifest displays the default icon with the correct size.
NWJS: v0.13.2 SDK
OS: Win7x64
When setting a custom icon for the app in the manifest
"window":{"icon": "icon.png"}, it will show with an incorrect size under the volume mixer.The following example shows the result of a simple app playing a YouTube video and the custom icon used in the manifest is NWJS's own icon. The icon displayed in the volume mixer is too big as you can see:
Not using a custom icon in the manifest displays the default icon with the correct size.
NWJS: v0.13.2 SDK
OS: Win7x64