Hi Matthew,
Just to be sure, you are trying to do this for the rich text fields on the admin side, correct? Admin uses CKEditor while the live site uses Froala so I am just double checking.
If it is in fact for the admin, my guess is that you still need to add the selector into the toolbar. So in this case, you would just need to add in ['Font'] somewhere in your toolbar configuration like so:
Can you try this and let me know if it helps?