Download the latest version from the Extension Mirror (I’m still waiting for it to be approved on Mozilla Update).
This release is a minimal update: ThunderBayes how displays a progress bar while messages are being processed.
However, I will note that I am very pleased with the results of using the extension. Before I started using ThunderBayes I got 10 to 15 spam emails in my inbox per day. Now I get one or two! All due to a simple and convenient method of training SpamBayes.