What sort of problems are you having, could you describe them? Which versions of Zimbra and Thunderbird. FWIW, I haven't seen any issues with Thunderbird on versions of Zimbra 3.1.2 through to the current R4 RC1.
Found the problem.
It was not a Zimbra problem but a AntiVirus software problem.
F-Secure was interfering with Thunderbird.
After disabling the mail scan all was well.
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SamTzu
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"I keep hitting the esc key, why am I still here?"