Since yesterday there is an update available for Silverlight 2 . This update improves stability, media streaming, and the auto-update component. This update also improves support for Firefox 3 .
Microsoft Support kb955011 
More details on Silverlight and Firefox 3 for Web developers:
When visiting download Web page of Silverlight  I get the message that the latest Silverlight 2 plugin is installed (version 2.0.30523.6). After installing the Silverlight update using update.microsoft.com  I have version 2.0.30523.8, now.