how to install on thunderbird 7 and higher Rated 5 out of 5 stars
great tool - gives structure to endless replied & replied emails ;-)
but how to install on thunderbird 6/7/8/.. and higher?
well, use vim, which is able to edit ziped xpi files.
inavigate to: install.rdf
and change <em:maxVersion>7.*</em:maxVersion>
save & install it!