lib/less-browser/bootstrap.js
function resolveOrReject(data) {
    if (data.filename) {
        console.warn(data);
    }
    if (!options.async) {
        head.removeChild(style);
    }
}
function resolveOrReject(data) {
    if (data.filename) {
        console.warn(data);
    }
    if (!options.async) {
        head.removeChild(style);
    }
}
Always restore page visibility