Hello! 1. Sorry for delay with answer. 2. Can't download a new version for FF from FTP that you say. 3. Now use this for my purposes: https://addons.mozilla.org/en-US/firefox/addon/encode-decode-base64/?src=api
The xpi file published in http://ftp.oops.org/pub/Windog/Firefox/Extension/rightencoding/rightencoding-0.2.5.xpi doesn't support Thunderbirtd8 because the maxVersion in install.rdf is 8.0.x, which should be of 8.0.*, so thunderbird 8 doesn't recognize it
This review is for a previous version of the add-on (0.2.5.1-signed).