@font-face src: local - How to use the local font if the user already has it?

Question

What is the right way to use @font-face so that the browser will not download the font if the user already have it?

I am using @font-face to define Deja

Answer 1

If you want to check for local files first do:

@font-face {
font-family: 'Green Sans Web';
src:
    local('Green Web'),
    local('GreenWeb-Regular'),
    url('GreenWeb.ttf');
}

There is a more elaborate description of what to do here.