That article notes that the characters it escapes are just a sample of the special characters, and there are actually many more characters to escape.

This [blog post](http://mathiasbynens.be/notes/css-escapes) describes them all, and this [unlicensed codebase](https://github.com/mathiasbynens/mothereff.in/tree/master/css-escapes) implements an escaper. But its code is quite large and complicated, so I think we're better off using a different API than *querySelector* to retrieve the frame in question, even though *querySelector* is an elegant way of doing so.

For example, we could use something like the following code:

```
    let iframe = Array.prototype.filter.call(
      shell.contentBrowser.contentDocument.getElementsByTagName("iframe"),
      function(iframe) iframe.getAttribute("data-frame-origin") == origin
    )[0];
```