Rated 5 out of 5 stars
Seems to be working even with TB3. I removed the plugin from TB. Then I opened the installation file (correct_identity-1.3.1-tb.xpi) with a zip-programme (or simply rename it to .zip and later don't forget to rename again to .xpi) and edited the install.rdf (open it with a text editor).
Then save the file and install the addon in thunderbird.