We had several users report that Zimbra wasn't displaying properly this afternoon. We realized that only Firefox 3.6.3 users were affected, and then
discovered that only people with the 'beach' theme had problems.
We ended up turning off 'beach' in the COS and making the default 'sand',
so all of the impacted Firefox users can now log in again. If we re-enable 'beach' and use the skin previewer zimlet the problem becomes apparent
For now we'll leave 'beach' off.