Rated 3 out of 5 stars
Not a bad addon, with one exception.
Using the method discussed in previous comments, i changed the max version to 3.0. I am running Thunderbird 188.8.131.52, and after i installed the (modified) add-on, all my message headers disappeared, the window and everything. This could also be due to the fact that i also have many other add-ons installed. I tried disabling them, but the only way to get the headers bar back was to uninstall Notary.