Well since "ZaXFormViewController.prototype.fireChangeEve nt" doesn't seem to be in any bug's description on bugzilla, and in the 3 other threads with this error there is no solution, my guess would be nobody who is able to fix it knows about it.
Please file a bug in
Bugzilla Main Page - Zimbra and post a link here so people searching in the future can find it.
For your information here are the other threads listing the exact same issue:
ZIMBRA down when pop field is written [SOLVED] zcs-5.0.18_GA to zcs-6.0.2_GA - stats not running and CPU load spikes... zcs 6.0.2 with external LDAP authentication?