Firefox?

put this after edge:

function uabc_isFF() {
    $cn_uabc_isFF= (bool) strpos($_SERVER['HTTP_USER_AGENT'],'Firefox');
    if ($cn_uabc_isFF)
        return true;
    else return false;
}

and change this:

        // Desktop
        if(uabc_isFF()) $classes[] = 'browser-firefox';
        elseif($is_gecko) $classes[] = 'browser-gecko';

this works for me!
THX