Thunderbird slow

Hallo,
since some weeks my Mozilla Thunderbird 2.0.0.21 has become very slow visualizing some html mail (like paypal payment's one).

Before it wasn't so slow but now it takes even one minute when I select one of them but only the first time: if i select it again is much faster.
I think it is because it tries to show the remote images that are in the mail.

I have done some things, even if maybe are not useful: I have zipped the mail, emptied the incremental filter of the undesidered mail, reinstalled the program and disabled the antivirus; I have checked too that in configuration editor was flagged the mailnews message display disable remote image but nothing has changed.

Which can be the reason?

Thank you

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