When using a custom "Emoji Source" location the files are hard-coded for the png extension. This option allow you to select a different extension such as svg. (See thread 177937 at XenForo.com for reference.)
This is a small add-on that will change the file extension of emoji images when served from a custom CDN. For our sites we serve the emoji images from our own locations and use .SVG images.
Read the FAQ for an example of how to use Twitter's Twemoji .SVG images for your emoji...
