0.90.2.0 is installed with the latest mozilla-tb ebuild, whereas 0.91.0 has been out since march. this version includes a number of bugfixes and "New support for OpenPGP: MIME header"
Enigmail 0-92 is already out, but isn't available through portage nor through Thunderbird's ebuild
agriffis gave me permission to fix this
...aaaannnnndddd fixed