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 DejaVu, which is already installed on my system (linux).
Firefox is not downloading the font, but Chromium is downloading it every time!

My CSS code, based on font squirrel and that question look like this:

@font-face {
    font-family: 'DejaVu Serif';
    src: url('DejaVuSerif-webfont.eot');
    src: local('DejaVu Serif'), url('DejaVuSerif-webfont.woff') format('woff'), url('DejaVuSerif-webfont.ttf') format('truetype'), url('DejaVuSerif-webfont.svg#webfontCFu7RF0I') format('svg');
    font-weight: normal;
    font-style: normal;
}

/* ... @font-face definitions for italic and bold omitted ... */

@font-face {
    font-family: 'DejaVu Serif';
    src: url('DejaVuSerif-BoldItalic-webfont.eot');
    src: local('DejaVu Serif Bold Italic'), url('DejaVuSerif-BoldItalic-webfont.woff') format('woff'), url('DejaVuSerif-BoldItalic-webfont.ttf') format('truetype'), url('DejaVuSerif-BoldItalic-webfont.svg#webfontQAewh7pf') format('svg');
    font-weight: bold;
    font-style: italic;
}

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.