It seems that font-awesome icons will work if you upload them as svg files. 
I am surprised that they are displaying inline correctly. I don’t know if you can count on them doing that.
You can get the icons here: Font-Awesome-SVG-PNG/black/svg at master · Rush/Font-Awesome-SVG-PNG · GitHub The icons seem to default to width="500" height="500" To display them at a smaller size, you need to edit those values. The icons in this post are set to width="45"height=“45”
To get it to work you need to add svg to the authorized extensions in admin>files