We recently upgraded to ZCS from 5.0.18 and Firefox is the only browser that works for email. All versions of IE, Safari and even Chrome do not work. When the user logs in with one of the non-working browsers, it stays locked up at the loading page. Clearing browser history and cache has no effect.

There doesn't appear to be any errors in /opt/zimbra/logs/mailbox.log

Any help would be appreciated.