var nodes = document.evaluate('//body//text()', document, null, 6, null),
    validRange, node, text, j, i, charText;



// -------------------------- EDIT FONT HERE --------------------------
GM_addStyle('' +
    '.non-uni-text { ' +
        'font-family: "Dejavu Sans" !important; ' +
    '}' +
'');
// ------------------------ / EDIT FONT HERE --------------------------



for (j = 0; node = nodes.snapshotItem(j); j += 1) {
    text = node.data;
    validRange = true;

    for (i = 0; i < text.length; i += 1) {
        // 55203 is the last unicode character Dejavu Sans supports
        if (text.charAt(i).charCodeAt(0) > 55203) {
            validRange = false;
        }
    }

    if (validRange) {
        node.parentNode.classList.add('non-uni-text');
    }
}