thunderbird portableapps moving, deleting and viewing mail really slow

Hi,

I have thunderbird portable running against a dovecot IMAP server on fedora core 6. It has recently got progressively slower until now its almost unusable. Initially I thought this was a problem with dovecot, so I spent some time checking dovecot performance and indexes. However I have tried connecting to my IMAP mail server using Outlook express, evolution on linux and from a Horde/IMP webmail account, and these are all acceptable performance times and it seems to be that thurderbird is the culprit.

I have not got a local install of thunderbird to compare against the portable apps one, and trying to install it locally seems to just try to install it over the portableapps one.

I was wondering whether anyone has any suggestions to troubleshoot this problem, and any idea whether its portable apps specific or a thunderbird thing?

Thanks,

Tom