It can be enabled in Seamonky 2.10 Rated 4 out of 5 stars

It worked with Seamonkey 2.9.1 but after the automatic update Seamonkey 2.10 disabled Seazilla 2.4 and it could not be enabled. I installed Disable Add-on Compatibility Checks 1.3 and Seazilla works again.
https://addons.mozilla.org/en-us/thunderbird/addon/checkcompatibility/

In Composer the print button icon is badly distorted, everything else looks and works fine.

Zanqeutil

This user has 4 previous reviews of this add-on.