Rated 5 out of 5 stars

Note that Nostalgy has been ported to TB78 recently under the name of "Nostalgy++":

https://addons.thunderbird.net/de/thunderbird/addon/nostalgy_ng/

There was/is still one (major) issue with a keyboard shortcut - for details, see https://github.com/opto/nostalgy-xpi/issues/29)

Apart from this, my experience so far is positive.

This user has a previous review of this add-on.