[9dev]

That would be:

  @font-face {
      font-family: 'foo';
      src: url(data:application/x-font-woff;charset=utf-8;base64,d09GRgABAAAAAGy …)
  }

[jfk13]

A minor detail, but the MIME type should be `font/woff` (or `font/woff2` if appropriate), not the nonstandard `application/x-...`.

(E.g. see https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_...)