Twitter @anywhere API problems in firefox only

I've implemented a simple example of the Twitter @anywhere api to display user hovercards. The example works great in Internet Explorer and Chrome. However, whenever I the page loads in Firefox I receive the following message in an alert window:

To set up @anywhere, please provide a client ID

Surely if the results are correct in Chrome and IE then everything must be setup correctly?

Here is a simple code block which I've tested recreates the problem in Firefox only:

&l开发者_如何学Got;script src="http://platform.twitter.com/anywhere.js?id=WMg5kRMlIw807lRTsktnNQ&v=1" type="text/javascript" >
</script>
<script type="text/javascript">
 twttr.anywhere(onAnywhereLoad);
 function onAnywhereLoad(twitter) {
    twitter().hovercards();
 }); 
</script>

This problem is showing up in various forums and mailing lists. I'm seeing it on Firefox 3.0.5 (but not 3.6). Looks like Twitter didn't do enough testing before springing this one on the world.

(Later: Try clearing hour cookies. Yeah, that's a very 90's thing to have to do.)