Hey,
you need to add the font to the option panel. Open up brightbox\includes\admin\register-admin-options.php
and search for following code:
"subtype" => array( 'Arvo'=>'arvo',
'Bevan'=>'bevan',
'Cantarell'=>'cantarell',
'Cardo'=>'cardo',
'Droid Sans'=>'droidsans',
'Inconsolata'=>'inconsolata',
'Josefin All Characters'=>'josefine',
'Josefin Common Characters'=>'josefine_small',
'Kreon'=>'kreon',
'Lobster'=>'lobster',
'Molengo'=>'molengo',
'Oswald'=>'oswald',
'Reenie Beanie'=>'reeniebeanie__1.4', //number attached is a font size modifier for very small fonts ( * 1.4)
'Tangerine'=>'tangerine__1.6',
'Vollkorn'=>'vollkorn',
'Yanone Kaffeesatz'=>'yanonekaffeesatz'
));
Add your font to it. First text is the name of the font (how it will display in the user interface) and second text the name of the file without .font.js extension.