How to customize a page's unicode (emicode)?

In Windows operating systems when using emojis the font used by browsers usually is Segoe UI Emoji

  

Note: in Firefox it has its own "emojis system", I think it uses Twemoji Mozilla :   - link

     

What makes Firefox have its own emojis, without relying on operating system support

Is it possible via CSS and external fonts to customize the emoji of a page?

This is without using images and the like, the idea is really to use emojis unicode