Google jspai fails to load, but only for customer

My website needs to use the Google Earth plugin for just a bit longer (I know, the API is deprecated, but I'm stuck with it for several more months). I load it by including google.com/jsapi, then calling google.load like so:

    ...
    <script type="text/javascript" src="http://ift.tt/JuZcy0"></script>
    <script type="text/javascript">
        google.load("earth", "1", {"other_params": "sensor=false"});
        google.setOnLoadCallback(function () {
            // call some JavaScript to begin initializing the GE plugin
        });
    </script>
</body>
</html>

This works well from multiple computers and with multiple browser inside our company's firewall. It works well from my home computer, and from my colleagues' home computers. However, when my customer tries to load it, she gets an error message that google is not defined on the line that begins google.load(.

Of course, global variable google is defined at the start of file www.google.com/jsapi, so presumably that file isn't loading. I initially assumed that her corporate firewall was blocking that file, but when I asked her to paste "http://ift.tt/JuZcy0" into her browser's address bar, she said that immediately loaded up a page of JavaScript.

The entire output to the browser console is:

Invalid URI. Load of media resource  failed. main.html
ReferenceError: google is not defined main.html:484

And I believe the Invalid URI business is just because we don't have a favicon.ico file.

She is running Firefox 35.0.1, though she says the same error occurred with IE (she didn't mention the version of IE).

Short of asking her to install Firebug, which I don't think is going to be feasible, how can I troubleshoot this issue?