Great but... Rated 5 out of 5 stars

Either Thunderbird 38.1 broke QF [got 4.1.1] or QF needs updating to the latest TB code, but the messages view but for the header in text, have become unviewable with QF loaded. Disable the Add-On and the messages show fine. It works fine with 31.n on another machine.

Edit: The PTF was to remove the add-on, which returned all mail in full view, not only the header in text format, but complete rendering. After restarting twice and adding QF back the mail view returned. An essential add-on to me :D

This review is for a previous version of the add-on (4.1.1). 

Please raise a bug:

...here:
http://quickfolders.mozdev.org/bugs.html

also if you could upload or send me a screenshot that would be great. Usually a trip to the QuickFolders "bling my tabs" settings page and choosing some colors will fix any unforeseen display issues. Sometimes font and background color can coincide in unpredictable ways.