Rated 2 out of 5 stars

Warning: I tried to uninstall/disable this add-on an it left my headers a mess. Bug reported.
EDIT: Just in case someone else faces the same problem, here's how I workaround to revert this (disclaimer untested but seems to work. At your own risk!):

* Uninstall the add-on
* Open the Config Editor: Edit > Preferences > General > Config Editor...
* Locate the mailnews.headers.extraExpandedHeaders parameter and enter an empty string
* Locate the extensions.maillistfilter.origExtraExpandedHeaders parameter and enter an empty string