Rated 5 out of 5 stars

by Rob2 on Jan. 31, 2019 ·

Got it to work on 60.5.0. The trick is noted below in one of the other reviews -
http://kb.mozillazine.org/Editing_an_add-on_to_change_its_compatibility

I first installed 7-zip, then used it to change the maxVersion in the install.rdf file from 14.0a1 to 99.0. Make sure to save changes. Then install the addon from the changed xpi file. This also required a restart of Thunderbird (it prompted me with a handy button).